/* ---------- theme ---------- */
:root{
  --bg:#0A0C12; --bg-1:#0E111A; --bg-2:#151924; --bg-3:#1B2029;
  --glass:rgba(255,255,255,.04); --glass-hover:rgba(255,255,255,.07);
  --border:rgba(255,255,255,.09); --border-strong:rgba(255,255,255,.18);
  --text:#F3F4F7; --text-2:#A7ADBA; --text-3:#6C7280;
  --accent-a:#7C93FF; --accent-b:#2DD9C9;
  --grad:linear-gradient(135deg,var(--accent-a) 0%,var(--accent-b) 100%);
  --tool:#2DD9C9; --warn:#F5B84E; --danger:#F0715C;
  --topbar-bg:rgba(10,12,18,.75);
  --shadow-lg:0 20px 45px rgba(0,0,0,.5);
  --on-grad:#0A0C12;
  --r-sm:8px; --r-md:12px; --r-lg:18px; --r-xl:22px;
  --font-display:'Bricolage Grotesque',sans-serif;
  --font-body:'Inter',sans-serif;
  --font-mono:'JetBrains Mono',monospace;
}
html[data-theme="light"]{
  --bg:#FFFFFF; --bg-1:#F1F3F8; --bg-2:#FFFFFF; --bg-3:#E9ECF3;
  --glass:rgba(16,20,32,.03); --glass-hover:rgba(16,20,32,.06);
  --border:rgba(16,20,32,.11); --border-strong:rgba(16,20,32,.22);
  --text:#131722; --text-2:#4A5163; --text-3:#7A8296;
  --accent-a:#4F63D2; --accent-b:#0E9C8D;
  --tool:#0E9C8D; --warn:#B87A16; --danger:#C4472F;
  --topbar-bg:rgba(251,251,253,.82);
  --shadow-lg:0 18px 40px rgba(16,20,32,.14);
  --on-grad:#FFFFFF;
}
html[data-theme="light"] body{background:var(--bg);}
html[data-theme="light"] .blob{opacity:.18;}
html[data-theme="light"] .quiz-opt{background:var(--bg-2);}
html[data-theme="light"] .brand-mark{color:#fff;}
html[data-theme="light"] ::selection{background:rgba(79,99,210,.18);color:#131722;}

*{box-sizing:border-box;}
html,body{margin:0;padding:0;}
body{font-family:var(--font-body);background:var(--bg);color:var(--text);-webkit-font-smoothing:antialiased;overflow-x:hidden;}
a{color:inherit;text-decoration:none;}
button{font-family:inherit;cursor:pointer;}
::selection{background:rgba(124,147,255,.3);color:#fff;}
:focus-visible{outline:2px solid var(--accent-a);outline-offset:2px;}

/* ---------- shell ---------- */
.shell{display:grid;grid-template-rows:60px 1fr;grid-template-columns:272px 1fr;
  grid-template-areas:"header header" "sidebar main";min-height:100vh;}

/* ---------- header ---------- */
.topbar{grid-area:header;background:var(--topbar-bg);backdrop-filter:blur(16px);
  border-bottom:1px solid var(--border);display:flex;align-items:center;gap:18px;
  padding:0 20px;position:sticky;top:0;z-index:40;}
.brand{display:flex;align-items:center;gap:9px;font-family:var(--font-display);font-weight:700;font-size:16px;flex-shrink:0;}
.brand-mark{width:27px;height:27px;border-radius:8px;background:var(--grad);display:flex;
  align-items:center;justify-content:center;font-family:var(--font-mono);font-size:11.5px;font-weight:600;color:var(--on-grad);}
.divider-v{width:1px;height:24px;background:var(--border);flex-shrink:0;}
.dot-ring{width:22px;height:22px;border-radius:50%;display:flex;align-items:center;justify-content:center;
  background:rgba(45,217,201,.2);flex-shrink:0;}
.dot-ring.sm{width:20px;height:20px;}
.tool-dot{width:8px;height:8px;border-radius:50%;background:var(--tool);}

.tool-switch{position:relative;flex-shrink:0;}
.tool-switch-btn{display:flex;align-items:center;gap:10px;background:var(--glass);border:1px solid var(--border);
  border-radius:var(--r-md);padding:6px 12px 6px 8px;color:var(--text);transition:border-color .15s,background .15s;}
.tool-switch-btn:hover{border-color:var(--border-strong);background:var(--glass-hover);}
.tool-switch-btn .name{font-family:var(--font-display);font-weight:600;font-size:14px;}
.tool-switch-btn .id{font-family:var(--font-mono);font-size:10.5px;color:var(--text-3);background:var(--bg-1);
  border:1px solid var(--border);border-radius:4px;padding:1px 6px;}
.tool-switch-btn .chev{color:var(--text-3);margin-left:2px;transition:transform .15s;}
.tool-switch.open .chev{transform:rotate(180deg);}
.tool-menu{position:absolute;top:calc(100% + 8px);left:0;width:290px;background:var(--bg-2);
  border:1px solid var(--border-strong);border-radius:var(--r-md);box-shadow:var(--shadow-lg);
  padding:6px;display:none;z-index:50;}
.tool-switch.open .tool-menu{display:block;}
.tool-menu-label{font-family:var(--font-mono);font-size:10px;letter-spacing:.06em;color:var(--text-3);
  padding:8px 10px 6px;text-transform:uppercase;}
.tool-option{display:flex;align-items:center;gap:10px;padding:9px 10px;border-radius:8px;color:var(--text);
  background:none;border:none;width:100%;text-align:left;}
.tool-option:hover{background:var(--glass-hover);}
.tool-option[aria-current="true"]{background:rgba(45,217,201,.1);}
.tool-option .name{font-family:var(--font-display);font-weight:600;font-size:13.5px;flex:1;}
.tool-option .count{font-family:var(--font-mono);font-size:11px;color:var(--text-3);}
.tool-option.disabled{opacity:.4;cursor:not-allowed;}
.tool-option.disabled:hover{background:none;}
.tool-menu-footer{border-top:1px solid var(--border);margin-top:6px;padding-top:6px;}
.browse-btn{display:flex;align-items:center;gap:8px;padding:9px 10px;border-radius:8px;color:var(--text-2);font-size:13px;font-weight:500;}
.browse-btn:hover{background:var(--glass-hover);color:var(--text);}

.search-wrap{flex:1;max-width:420px;margin-left:auto;position:relative;}
.search-wrap > svg{position:absolute;left:11px;top:15px;color:var(--text-3);}
.search-input{width:100%;background:var(--glass);border:1px solid var(--border);border-radius:var(--r-md);
  padding:8px 12px 8px 34px;color:var(--text);font-family:var(--font-mono);font-size:12.5px;}
.search-input::placeholder{color:var(--text-3);}
.search-input:focus{outline:none;border-color:var(--accent-a);background:var(--glass-hover);}
.kbd{position:absolute;right:9px;top:11px;font-family:var(--font-mono);font-size:10.5px;color:var(--text-3);
  border:1px solid var(--border);border-radius:4px;padding:1px 5px;}
.search-results{position:absolute;top:calc(100% + 8px);left:0;right:0;background:var(--bg-2);
  border:1px solid var(--border-strong);border-radius:var(--r-md);box-shadow:var(--shadow-lg);
  max-height:60vh;overflow-y:auto;display:none;z-index:60;padding:6px;}
.search-results.open{display:block;}
.sr-item{display:flex;align-items:center;gap:10px;padding:9px 11px;border-radius:8px;font-size:13px;color:var(--text-2);}
.sr-item:hover,.sr-item.sel{background:var(--glass-hover);color:var(--text);}
.sr-kind{font-family:var(--font-mono);font-size:9.5px;color:var(--text-3);border:1px solid var(--border);
  border-radius:4px;padding:1px 6px;flex-shrink:0;}
.sr-empty{padding:14px;color:var(--text-3);font-size:13px;text-align:center;}
.menu-toggle{display:none;background:none;border:none;color:var(--text);padding:6px;border-radius:6px;}
.menu-toggle:hover{background:var(--glass-hover);}

/* ---------- sidebar ---------- */
.sidebar{grid-area:sidebar;background:var(--bg-1);border-right:1px solid var(--border);
  padding:18px 12px;overflow-y:auto;position:sticky;top:60px;height:calc(100vh - 60px);}
.sb-identity{display:flex;align-items:center;gap:10px;padding:10px;margin-bottom:16px;
  background:var(--glass);border:1px solid var(--border);border-radius:var(--r-md);}
.sb-identity .dot-ring{width:30px;height:30px;}
.sb-identity .tool-dot{width:11px;height:11px;}
.sb-identity-name{font-family:var(--font-display);font-weight:600;font-size:14px;}
.sb-identity-sub{font-family:var(--font-mono);font-size:10.5px;color:var(--text-3);}
.sb-group{margin-bottom:20px;}
.sb-group-label{font-family:var(--font-mono);font-size:10.5px;letter-spacing:.07em;text-transform:uppercase;
  color:var(--text-3);padding:0 10px 8px;}
.sb-item{position:relative;display:flex;align-items:center;gap:10px;padding:9px 10px 9px 13px;border-radius:9px;
  color:var(--text-2);font-size:13.5px;font-weight:500;margin-bottom:2px;transition:background .12s,color .12s;}
.sb-item:hover{background:var(--glass);color:var(--text);}
.sb-item.active{background:linear-gradient(135deg,rgba(124,147,255,.14),rgba(45,217,201,.14));color:var(--text);}
.sb-item.active::before{content:'';position:absolute;left:0;top:8px;bottom:8px;width:3px;border-radius:3px;background:var(--grad);}
.sb-item svg{flex-shrink:0;opacity:.7;}
.sb-item.active svg{opacity:1;}
.sb-item .label{flex:1;}
.sb-item .count{font-family:var(--font-mono);font-size:11px;color:var(--text-3);}
.sb-item.active .count{color:var(--text-2);}
.new-badge{font-family:var(--font-mono);font-size:9px;font-weight:600;background:rgba(45,217,201,.16);
  color:var(--tool);border-radius:5px;padding:2px 5px;}
.sb-footer{margin-top:10px;padding:14px 12px;border-top:1px solid var(--border);}
.sb-footer-title{font-family:var(--font-display);font-weight:600;font-size:12.5px;margin-bottom:8px;}
.progress-track{height:5px;border-radius:4px;background:var(--glass);overflow:hidden;margin-bottom:7px;}
.progress-fill{height:100%;width:100%;background:var(--grad);border-radius:4px;}
.sb-footer-sub{font-size:11.5px;color:var(--text-3);}

/* ---------- main ---------- */
.content{grid-area:main;padding:36px 44px 90px;max-width:900px;}
.breadcrumb{font-family:var(--font-mono);font-size:12px;color:var(--text-3);margin-bottom:22px;
  display:flex;align-items:center;gap:6px;flex-wrap:wrap;}
.breadcrumb a:hover{color:var(--text-2);}
.breadcrumb .sep{color:var(--border-strong);}
.breadcrumb .current{color:var(--text-2);}

.page-head{margin-bottom:26px;}
.page-head h1{font-family:var(--font-display);font-weight:600;font-size:32px;line-height:1.2;letter-spacing:-.015em;margin:0 0 10px;}
.lede{font-size:15.5px;line-height:1.65;color:var(--text-2);margin:0;max-width:62ch;}

.q-header{display:flex;align-items:flex-start;justify-content:space-between;gap:20px;margin-bottom:16px;}
.q-title{font-family:var(--font-display);font-weight:600;font-size:29px;line-height:1.25;letter-spacing:-.01em;margin:0;}
.pill{font-family:var(--font-mono);font-size:11px;font-weight:500;padding:4px 10px;border-radius:20px;
  white-space:nowrap;flex-shrink:0;border:1px solid transparent;}
.pill-beginner{background:rgba(45,217,201,.12);color:#5FE0D3;border-color:rgba(45,217,201,.25);}
.pill-intermediate{background:rgba(245,184,78,.12);color:var(--warn);border-color:rgba(245,184,78,.25);}
.pill-advanced{background:rgba(240,113,92,.12);color:var(--danger);border-color:rgba(240,113,92,.25);}
.field-tags{display:flex;gap:8px;margin-bottom:30px;flex-wrap:wrap;}
.field-tag{font-family:var(--font-mono);font-size:11px;color:var(--text-3);border:1px solid var(--border);
  padding:3px 9px;border-radius:5px;}
.field-tag:hover{color:var(--text-2);border-color:var(--border-strong);}

.block{margin-bottom:32px;}
.block-label{font-family:var(--font-mono);font-size:11px;letter-spacing:.06em;text-transform:uppercase;
  color:var(--tool);margin-bottom:12px;display:flex;align-items:center;gap:8px;}
.block-label::after{content:'';flex:1;height:1px;background:var(--border);}
.answer{font-size:15.5px;line-height:1.8;color:var(--text-2);}
.answer p{margin:0 0 15px;}
.answer strong{font-weight:600;color:var(--text);}
.answer em{color:var(--text);}
.answer ul{margin:0 0 15px;padding-left:20px;}
.answer li{margin-bottom:8px;}
.answer code{font-family:var(--font-mono);background:var(--bg-2);border:1px solid var(--border);
  padding:1px 6px;border-radius:4px;font-size:.9em;color:var(--text);}
.answer a{color:var(--accent-a);text-decoration:underline;text-underline-offset:2px;}

.related-grid{display:flex;flex-wrap:wrap;gap:9px;}
.related-chip{display:flex;align-items:center;gap:7px;font-size:13px;padding:9px 14px;border:1px solid var(--border);
  border-radius:9px;background:var(--glass);color:var(--text-2);transition:border-color .12s,transform .12s,color .12s;}
.related-chip:hover{border-color:var(--tool);color:var(--text);transform:translateY(-1px);}
.related-chip svg{color:var(--text-3);flex-shrink:0;}

.q-footer{display:flex;align-items:center;justify-content:space-between;gap:16px;margin-top:48px;
  padding-top:22px;border-top:1px solid var(--border);}
.nav-link{display:flex;align-items:center;gap:8px;font-size:13px;font-weight:500;color:var(--text-3);max-width:46%;}
.nav-link:hover{color:var(--text-2);}
.nav-link.next{margin-left:auto;text-align:right;}
.nl-text{overflow:hidden;text-overflow:ellipsis;white-space:nowrap;}

/* stat strip */
.stat-strip{display:flex;gap:10px;margin-bottom:34px;flex-wrap:wrap;}
.stat{background:var(--glass);border:1px solid var(--border);border-radius:var(--r-md);
  padding:12px 18px;display:flex;flex-direction:column;gap:2px;min-width:96px;}
.stat b{font-family:var(--font-display);font-size:21px;font-weight:600;}
.stat span{font-family:var(--font-mono);font-size:10.5px;color:var(--text-3);}

/* category blocks */
.cat-block{margin-bottom:34px;scroll-margin-top:80px;}
.cat-head{display:flex;align-items:flex-end;justify-content:space-between;gap:16px;
  padding-bottom:12px;margin-bottom:14px;border-bottom:1px solid var(--border);}
.cat-head h2{font-family:var(--font-display);font-weight:600;font-size:18px;margin:0 0 3px;}
.cat-head p{margin:0;font-size:13px;color:var(--text-3);}
.cat-count{font-family:var(--font-mono);font-size:12px;color:var(--text-3);
  background:var(--glass);border:1px solid var(--border);border-radius:20px;padding:3px 11px;flex-shrink:0;}
.q-list{display:flex;flex-direction:column;gap:2px;}
.q-row{display:flex;align-items:center;justify-content:space-between;gap:14px;padding:12px 14px;
  border-radius:10px;border:1px solid transparent;transition:background .12s,border-color .12s;}
.q-row:hover{background:var(--glass);border-color:var(--border);}
.q-row-title{font-size:14.5px;color:var(--text-2);}
.q-row:hover .q-row-title{color:var(--text);}

/* index cards */
.idx-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(240px,1fr));gap:14px;}
.idx-card{background:var(--glass);border:1px solid var(--border);border-radius:var(--r-lg);padding:18px;
  display:flex;flex-direction:column;gap:9px;transition:transform .15s,border-color .15s,background .15s;}
.idx-card:hover{transform:translateY(-3px);border-color:var(--border-strong);background:var(--glass-hover);}
.idx-card-top{display:flex;}
.idx-kind{font-family:var(--font-mono);font-size:9.5px;letter-spacing:.04em;text-transform:uppercase;
  color:var(--tool);background:rgba(45,217,201,.1);border:1px solid rgba(45,217,201,.2);
  border-radius:20px;padding:3px 9px;}
.idx-card h3{font-family:var(--font-display);font-weight:600;font-size:15px;margin:0;line-height:1.35;}
.idx-card p{margin:0;font-size:13px;line-height:1.55;color:var(--text-3);}

/* glossary */
.gloss-list{display:flex;flex-direction:column;gap:2px;}
.gloss-row{display:grid;grid-template-columns:210px 1fr;gap:18px;padding:14px;border-radius:10px;
  border:1px solid transparent;transition:background .12s,border-color .12s;}
.gloss-row:hover{background:var(--glass);border-color:var(--border);}
.gloss-term{font-family:var(--font-display);font-weight:600;font-size:14.5px;}
.gloss-def{font-size:13.5px;line-height:1.6;color:var(--text-3);}
.gloss-row:hover .gloss-def{color:var(--text-2);}

/* empty state */
.empty-state{background:var(--glass);border:1px dashed var(--border-strong);border-radius:var(--r-xl);
  padding:48px 32px;text-align:center;display:flex;flex-direction:column;align-items:center;gap:12px;}
.empty-icon{width:48px;height:48px;border-radius:14px;background:var(--glass);border:1px solid var(--border);
  display:flex;align-items:center;justify-content:center;color:var(--text-2);}
.empty-state h2{font-family:var(--font-display);font-weight:600;font-size:18px;margin:4px 0 0;}
.empty-state p{margin:0;font-size:13.5px;line-height:1.6;color:var(--text-3);max-width:44ch;}
.btn-primary{margin-top:10px;font-size:13.5px;font-weight:600;padding:10px 18px;border-radius:10px;
  background:var(--grad);color:var(--on-grad);}
.btn-primary:hover{filter:brightness(1.08);}

/* ---------- home ---------- */
.home-header{position:sticky;top:0;z-index:50;display:flex;align-items:center;gap:14px;padding:0 28px;height:64px;
  background:rgba(10,12,18,.72);backdrop-filter:blur(16px);border-bottom:1px solid var(--border);}
.home-nav{display:flex;gap:2px;margin-left:10px;margin-right:auto;}
.home-nav a{font-size:14px;font-weight:500;color:var(--text-2);padding:8px 13px;border-radius:9px;}
.home-nav a:hover{color:var(--text);background:var(--glass);}
.header-cta{font-size:13.5px;font-weight:600;padding:9px 16px;border-radius:10px;
  background:var(--grad);color:var(--on-grad);flex-shrink:0;}
.header-cta:hover{filter:brightness(1.08);}
.hero{position:relative;padding:26px 28px 40px;text-align:center;overflow:hidden;}
.blob{position:absolute;border-radius:50%;filter:blur(90px);opacity:.28;pointer-events:none;z-index:0;}
.blob-a{width:520px;height:520px;background:var(--accent-a);top:-220px;left:8%;}
.blob-b{width:480px;height:480px;background:var(--accent-b);top:-180px;right:6%;}
.hero>*{position:relative;z-index:1;}
.hero>.blob{position:absolute;z-index:0;}
.eyebrow{display:inline-flex;align-items:center;gap:8px;font-family:var(--font-mono);font-size:12px;
  color:var(--text-2);background:var(--glass);border:1px solid var(--border);border-radius:30px;
  padding:6px 14px 6px 10px;margin-bottom:18px;}
.live-dot{width:6px;height:6px;border-radius:50%;background:var(--accent-b);animation:pulse 2s ease-in-out infinite;}
@keyframes pulse{0%,100%{opacity:1;box-shadow:0 0 0 0 rgba(45,217,201,.4);}50%{opacity:.7;box-shadow:0 0 0 5px rgba(45,217,201,0);}}
.hero-title{font-family:var(--font-display);font-weight:700;font-size:52px;line-height:1.08;
  letter-spacing:-.02em;margin:0 0 18px;}
.grad-text{background:var(--grad);-webkit-background-clip:text;background-clip:text;color:transparent;}
.hero-sub{font-size:16.5px;line-height:1.6;color:var(--text-2);max-width:560px;margin:0 auto 28px;}
.hero-actions{display:flex;gap:12px;justify-content:center;flex-wrap:wrap;margin-bottom:18px;}
.btn-ghost{font-size:14px;font-weight:600;padding:13px 22px;border-radius:12px;border:1px solid var(--border-strong);
  color:var(--text);background:var(--glass);}
.btn-ghost:hover{background:var(--glass-hover);}
.btn-lg{font-size:14px;font-weight:600;padding:13px 24px;border-radius:12px;background:var(--grad);color:var(--on-grad);}
.btn-lg:hover{filter:brightness(1.08);}
.status-line{font-family:var(--font-mono);font-size:12.5px;color:var(--text-3);display:flex;
  align-items:center;justify-content:center;gap:12px;flex-wrap:wrap;}
.status-line strong{color:var(--text-2);font-weight:600;}
.status-line .sep{color:var(--border-strong);}
.home-section{max-width:1100px;margin:0 auto;padding:44px 28px 20px;position:relative;z-index:1;}
.section-label{font-family:var(--font-mono);font-size:11.5px;letter-spacing:.08em;text-transform:uppercase;
  color:var(--text-3);margin-bottom:18px;display:flex;align-items:center;gap:12px;}
.section-label::after{content:'';flex:1;height:1px;background:var(--border);}
.tool-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:18px;}
.tool-card{position:relative;background:var(--glass);border:1px solid var(--border);border-radius:var(--r-xl);
  padding:24px;display:flex;flex-direction:column;gap:18px;transition:transform .18s,border-color .18s,box-shadow .18s,background .18s;}
.tool-card.active-tool:hover{transform:translateY(-5px);background:var(--glass-hover);
  border-color:var(--card-color);box-shadow:var(--shadow-lg);}
.tool-card::before{content:'';position:absolute;top:0;left:22px;right:22px;height:2px;
  background:var(--card-color,var(--border));border-radius:0 0 3px 3px;}
.tool-card.locked{opacity:.55;}
.tc-top{display:flex;align-items:flex-start;justify-content:space-between;gap:10px;}
.tc-id-block{display:flex;align-items:center;gap:11px;}
.tc-dot-ring{width:26px;height:26px;border-radius:50%;display:flex;align-items:center;justify-content:center;flex-shrink:0;}
.tc-dot{width:10px;height:10px;border-radius:50%;background:var(--card-color);}
.tc-name{font-family:var(--font-display);font-weight:600;font-size:18px;}
.tc-status{font-family:var(--font-mono);font-size:10px;font-weight:500;padding:4px 9px;border-radius:20px;
  white-space:nowrap;border:1px solid transparent;}
.status-active{background:rgba(45,217,201,.12);color:#5FE0D3;border-color:rgba(45,217,201,.25);}
.status-planned{background:var(--glass);color:var(--text-3);border-color:var(--border);}
.tc-desc{font-size:13.5px;line-height:1.6;color:var(--text-2);flex:1;}
.tc-stats{display:flex;gap:16px;font-family:var(--font-mono);font-size:11.5px;color:var(--text-3);
  border-top:1px solid var(--border);padding-top:15px;}
.tc-stats b{color:var(--text);font-weight:600;}
.tc-footer{display:flex;align-items:center;justify-content:space-between;font-size:12px;color:var(--text-3);}
.tc-enter{display:flex;align-items:center;gap:5px;font-weight:600;color:var(--card-color);}
.tc-enter svg{transition:transform .15s;}
.tool-card.active-tool:hover .tc-enter svg{transform:translateX(3px);}
.home-footer{margin-top:70px;border-top:1px solid var(--border);padding:34px 28px;display:flex;
  align-items:center;justify-content:space-between;flex-wrap:wrap;gap:16px;}
.footer-brand{display:flex;align-items:center;gap:9px;font-family:var(--font-display);font-weight:600;font-size:14px;}
.footer-links{display:flex;gap:22px;}
.footer-links a{font-size:12.5px;color:var(--text-3);}
.footer-links a:hover{color:var(--text-2);}

/* ---------- responsive ---------- */


@media (prefers-reduced-motion:reduce){*{animation:none !important;transition:none !important;}}

/* ---------- lessons ---------- */
.lesson-meta-top{display:flex;align-items:center;gap:10px;margin-bottom:14px;flex-wrap:wrap;}
.track-chip{font-family:var(--font-mono);font-size:11px;color:var(--tool);
  background:rgba(45,217,201,.1);border:1px solid rgba(45,217,201,.22);border-radius:20px;padding:4px 11px;}
.track-chip:hover{background:rgba(45,217,201,.16);}
.read-time{font-family:var(--font-mono);font-size:11.5px;color:var(--text-3);}
.lesson-lede{margin-bottom:26px;font-size:16px;}

.objectives{background:var(--glass);border:1px solid var(--border);border-left:2px solid var(--accent-a);
  border-radius:0 var(--r-md) var(--r-md) 0;padding:18px 22px;margin-bottom:34px;}
.obj-label{font-family:var(--font-mono);font-size:10.5px;letter-spacing:.06em;text-transform:uppercase;
  color:var(--text-3);margin-bottom:10px;}
.objectives ul{margin:0;padding-left:18px;}
.objectives li{font-size:14.5px;line-height:1.65;color:var(--text-2);margin-bottom:6px;}
.objectives li:last-child{margin-bottom:0;}

.lesson-body{margin-bottom:34px;}
.lesson-section{margin-bottom:30px;}
.lesson-section h2{font-family:var(--font-display);font-weight:600;font-size:19px;
  margin:0 0 12px;padding-bottom:9px;border-bottom:1px solid var(--border);}
.lesson-section p{font-size:15.5px;line-height:1.8;color:var(--text-2);margin:0 0 14px;}
.lesson-section strong{color:var(--text);font-weight:600;}
.lesson-section em{color:var(--text);}
.lesson-section code{font-family:var(--font-mono);background:var(--bg-2);border:1px solid var(--border);
  padding:1.5px 6px;border-radius:4px;font-size:.88em;color:var(--text);}
.lesson-section pre{background:var(--bg-2);border:1px solid var(--border);border-radius:var(--r-md);
  padding:14px 16px;overflow-x:auto;margin:0 0 14px;}
.lesson-section pre code{background:none;border:none;padding:0;font-size:12.5px;line-height:1.7;color:var(--text-2);}
.lesson-section ol{margin:0 0 14px;padding-left:22px;}
.lesson-section ol li{font-size:15px;line-height:1.75;color:var(--text-2);margin-bottom:6px;}

.keypoints{background:linear-gradient(135deg,rgba(124,147,255,.08),rgba(45,217,201,.08));
  border:1px solid var(--border);border-radius:var(--r-lg);padding:20px 24px;margin-bottom:34px;}
.kp-label{font-family:var(--font-mono);font-size:10.5px;letter-spacing:.06em;text-transform:uppercase;
  color:var(--tool);margin-bottom:11px;}
.keypoints ul{margin:0;padding-left:18px;}
.keypoints li{font-size:14.5px;line-height:1.65;color:var(--text-2);margin-bottom:7px;}
.keypoints li:last-child{margin-bottom:0;}

/* quiz */
.quiz-q{background:var(--glass);border:1px solid var(--border);border-radius:var(--r-lg);
  padding:20px 22px;margin-bottom:14px;}
.quiz-num{font-family:var(--font-mono);font-size:10.5px;color:var(--text-3);margin-bottom:8px;}
.quiz-text{font-size:15.5px;font-weight:500;line-height:1.55;margin-bottom:14px;}
.quiz-opts{display:flex;flex-direction:column;gap:8px;}
.quiz-opt{display:flex;align-items:flex-start;gap:10px;padding:11px 14px;border-radius:10px;
  border:1px solid var(--border);background:var(--bg-1);color:var(--text-2);font-size:14px;
  text-align:left;line-height:1.5;transition:border-color .12s,background .12s,color .12s;width:100%;}
.quiz-opt:hover:not(.locked){border-color:var(--border-strong);background:var(--glass-hover);color:var(--text);}
.quiz-opt .mk{font-family:var(--font-mono);font-size:11px;color:var(--text-3);flex-shrink:0;
  width:18px;height:18px;border-radius:5px;border:1px solid var(--border);
  display:flex;align-items:center;justify-content:center;margin-top:1px;}
.quiz-opt.correct{border-color:rgba(45,217,201,.5);background:rgba(45,217,201,.1);color:var(--text);}
.quiz-opt.correct .mk{border-color:rgba(45,217,201,.5);color:#5FE0D3;}
.quiz-opt.wrong{border-color:rgba(240,113,92,.5);background:rgba(240,113,92,.1);color:var(--text);}
.quiz-opt.wrong .mk{border-color:rgba(240,113,92,.5);color:var(--danger);}
.quiz-opt.locked{cursor:default;}
.quiz-exp{margin-top:12px;padding:12px 14px;border-radius:10px;background:var(--bg-2);
  border:1px solid var(--border);font-size:13.5px;line-height:1.6;color:var(--text-2);display:none;}
.quiz-exp.show{display:block;}
.quiz-score{font-family:var(--font-mono);font-size:12.5px;color:var(--text-2);
  background:var(--glass);border:1px solid var(--border);border-radius:10px;
  padding:12px 16px;margin-top:6px;display:none;}
.quiz-score.show{display:block;}

/* lesson list on hub */
.lesson-list{display:flex;flex-direction:column;gap:3px;}
.lesson-row{display:flex;align-items:center;justify-content:space-between;gap:18px;
  padding:14px;border-radius:11px;border:1px solid transparent;transition:background .12s,border-color .12s;}
.lesson-row:hover{background:var(--glass);border-color:var(--border);}
.lr-main{display:flex;flex-direction:column;gap:3px;min-width:0;}
.lr-title{font-size:15px;font-weight:500;color:var(--text);}
.lr-sum{font-size:13px;color:var(--text-3);line-height:1.5;}
.lr-meta{display:flex;align-items:center;gap:10px;flex-shrink:0;}


/* ---------- sidebar sub-tracks ---------- */
.sb-tracks{margin:2px 0 0 13px;padding-left:9px;border-left:1px solid var(--border);}
.sb-item.sb-sub{padding:6px 9px;font-size:12.5px;font-weight:400;color:var(--text-3);border-radius:7px;}
.sb-item.sb-sub:hover{color:var(--text-2);background:var(--glass);}
.sb-item.sb-sub::before{display:none;}

/* ---------- flashcards ---------- */
.flashdeck{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:14px;}
.flashcard{position:relative;min-height:150px;border-radius:var(--r-lg);cursor:pointer;
  border:1px solid var(--border);background:var(--glass);padding:20px;
  display:flex;flex-direction:column;justify-content:center;gap:10px;
  transition:border-color .15s,background .15s,transform .15s;text-align:left;width:100%;}
.flashcard:hover{border-color:var(--border-strong);background:var(--glass-hover);transform:translateY(-2px);}
.fc-side{font-family:var(--font-mono);font-size:9.5px;letter-spacing:.05em;text-transform:uppercase;color:var(--text-3);}
.fc-front{font-size:15px;font-weight:500;line-height:1.5;color:var(--text);}
.fc-back{font-size:14px;line-height:1.65;color:var(--text-2);display:none;}
.flashcard.flipped .fc-front{display:none;}
.flashcard.flipped .fc-back{display:block;}
.flashcard.flipped{border-color:var(--tool);background:var(--glass-hover);}
.fc-hint{font-family:var(--font-mono);font-size:10px;color:var(--text-3);margin-top:auto;}

/* ---------- exam ---------- */
.exam-bar{display:flex;align-items:center;gap:14px;flex-wrap:wrap;background:var(--glass);
  border:1px solid var(--border);border-radius:var(--r-md);padding:14px 18px;margin-bottom:20px;
  position:sticky;top:70px;z-index:20;backdrop-filter:blur(12px);}
.exam-prog{font-family:var(--font-mono);font-size:12.5px;color:var(--text-2);}
.exam-track{flex:1;height:5px;border-radius:4px;background:var(--bg-2);overflow:hidden;min-width:100px;}
.exam-fill{height:100%;width:0;background:var(--grad);border-radius:4px;transition:width .25s;}
.btn-submit{font-size:13px;font-weight:600;padding:9px 18px;border-radius:9px;
  background:var(--grad);color:var(--on-grad);border:none;}
.btn-submit:disabled{opacity:.4;cursor:not-allowed;}
.btn-reset{font-size:13px;font-weight:500;padding:9px 16px;border-radius:9px;
  background:var(--glass);border:1px solid var(--border);color:var(--text-2);}
.btn-reset:hover{color:var(--text);border-color:var(--border-strong);}
.exam-result{border-radius:var(--r-lg);padding:22px 24px;margin-bottom:20px;display:none;
  border:1px solid var(--border);background:linear-gradient(135deg,rgba(124,147,255,.1),rgba(45,217,201,.1));}
.exam-result.show{display:block;}
.exam-score{font-family:var(--font-display);font-size:30px;font-weight:600;margin-bottom:5px;}
.exam-verdict{font-size:14px;color:var(--text-2);}
.exam-q .quiz-opt.chosen{border-color:var(--border-strong);background:var(--glass-hover);color:var(--text);}
.exam-q .quiz-opt.chosen .mk{border-color:var(--accent-a);color:var(--accent-a);}

/* ---------- theme toggle ---------- */
.theme-toggle{display:flex;align-items:center;justify-content:center;
  width:34px;height:34px;flex-shrink:0;border-radius:9px;
  background:var(--glass);border:1px solid var(--border);color:var(--text-2);
  transition:color .15s,border-color .15s,background .15s;}
.theme-toggle:hover{color:var(--text);border-color:var(--border-strong);background:var(--glass-hover);}
.theme-toggle .icon-sun{display:none;}
html[data-theme="light"] .theme-toggle .icon-sun{display:block;}
html[data-theme="light"] .theme-toggle .icon-moon{display:none;}

/* ---------- three-column shell with lesson subnav ---------- */
.shell.has-subnav{grid-template-columns:250px 236px 1fr;
  grid-template-areas:"header header header" "sidebar subnav main";}

.subnav{grid-area:subnav;background:var(--bg-2);border-right:1px solid var(--border);
  padding:18px 10px;overflow-y:auto;position:sticky;top:60px;height:calc(100vh - 60px);}
.subnav-head{padding:0 10px 12px;margin-bottom:8px;border-bottom:1px solid var(--border);}
.subnav-title{font-family:var(--font-display);font-weight:600;font-size:13.5px;margin-bottom:3px;}
.subnav-sub{font-family:var(--font-mono);font-size:10.5px;color:var(--text-3);}
.subnav-track{margin-bottom:14px;}
.subnav-track-label{font-family:var(--font-mono);font-size:9.5px;letter-spacing:.07em;
  text-transform:uppercase;color:var(--text-3);padding:0 10px 6px;}
.subnav-item{position:relative;display:flex;align-items:flex-start;gap:9px;
  padding:7px 10px;border-radius:8px;font-size:12.8px;line-height:1.4;
  color:var(--text-2);margin-bottom:1px;transition:background .12s,color .12s;}
.subnav-item:hover{background:var(--glass);color:var(--text);}
.subnav-item.active{background:linear-gradient(135deg,rgba(124,147,255,.14),rgba(45,217,201,.14));
  color:var(--text);font-weight:500;}
.subnav-item.active::before{content:'';position:absolute;left:0;top:7px;bottom:7px;
  width:2.5px;border-radius:3px;background:var(--grad);}
.subnav-num{font-family:var(--font-mono);font-size:10px;color:var(--text-3);
  flex-shrink:0;min-width:15px;padding-top:1px;}
.subnav-item.active .subnav-num{color:var(--tool);}
.subnav-label{flex:1;}
.subnav-min{font-family:var(--font-mono);font-size:9.5px;color:var(--text-3);flex-shrink:0;padding-top:1px;}

/* narrower desktops: keep all three columns, just tighten them */

/* tablet: subnav becomes a slide-in drawer, opened from the sidebar */




html[data-theme="light"] .subnav{background:#FAFBFD;}
html[data-theme="light"] .sidebar{background:var(--bg-1);}
html[data-theme="light"] .topbar,html[data-theme="light"] .home-header{border-bottom-color:rgba(16,20,32,.13);}

/* ---------- narrow-screen top bar ---------- */



/* ---------- grid overflow containment ----------
   Grid/flex children default to min-width:auto, so a long code block or an
   unbreakable slug can force the whole track wider than the viewport. */
.shell{min-width:0;}
.content,.sidebar,.subnav{min-width:0;}
.content pre{max-width:100%;overflow-x:auto;}
.answer pre,.lesson-section pre{max-width:100%;overflow-x:auto;}
.breadcrumb{min-width:0;word-break:break-word;}
.q-title,.page-head h1,.lesson-section h2{overflow-wrap:break-word;}
.answer,.lesson-section p,.lr-sum,.tc-desc{overflow-wrap:break-word;}
.quiz-text,.quiz-opt,.gloss-def,.fc-front,.fc-back{overflow-wrap:break-word;min-width:0;}
.q-row,.lesson-row{min-width:0;}
.q-row-title,.lr-title{overflow-wrap:break-word;min-width:0;}
.topbar,.home-header{min-width:0;}
.search-wrap{min-width:0;}
.exam-bar{min-width:0;}

/* subnav header row + collapse control */
.subnav-head{display:flex;align-items:flex-start;justify-content:space-between;gap:8px;}
.subnav-close{display:none;align-items:center;justify-content:center;
  width:24px;height:24px;border-radius:6px;flex-shrink:0;
  background:var(--glass);border:1px solid var(--border);color:var(--text-3);}
.subnav-close:hover{color:var(--text);border-color:var(--border-strong);}
/* button in the sidebar that opens the drawer below 1000px */
.subnav-open-btn{display:none;align-items:center;gap:8px;width:100%;
  margin:0 0 12px;padding:9px 11px;border-radius:9px;font-size:12.8px;font-weight:500;
  background:var(--glass);border:1px solid var(--border);color:var(--text-2);}
.subnav-open-btn:hover{color:var(--text);border-color:var(--border-strong);}


/* keep these last: base rules above would otherwise win on equal specificity */



/* =====================================================================
   RESPONSIVE — single authoritative block. Keep it LAST in this file.
   Priority when space runs out: keep the lesson list, drop the section
   nav first. The lesson list is never display:none.
   ===================================================================== */

/* safety: nothing later may drop the blobs into normal flow */
.hero .blob{position:absolute;}

/* ---- 1180px: tighten the three columns ---- */
@media (max-width:1180px){
  .shell.has-subnav{grid-template-columns:216px 208px 1fr;}
  .sidebar{padding:16px 9px;}
  .subnav{padding:16px 8px;}
  .subnav-item{font-size:12.3px;padding:6px 9px;}
  .content{padding:30px 30px 80px;}
}

/* ---- 1000px: section nav becomes a drawer, lesson list stays in flow ---- */
@media (max-width:1000px){
  .shell.has-subnav{grid-template-columns:208px 1fr;
    grid-template-areas:"header header" "subnav main";}
  .shell.has-subnav .sidebar{position:fixed;top:60px;left:0;bottom:0;width:250px;z-index:38;
    transform:translateX(-100%);transition:transform .2s ease;box-shadow:var(--shadow-lg);}
  .shell.has-subnav .sidebar.open{transform:translateX(0);}
  .subnav{position:sticky;transform:none;box-shadow:none;}   /* stays visible */
  .menu-toggle{display:flex;align-items:center;}
  .subnav-open-btn,.subnav-close{display:none;}              /* no drawer needed */
  /* two-column pages (no subnav) collapse the sidebar the same way */
  .shell:not(.has-subnav){grid-template-columns:1fr;grid-template-areas:"header" "main";}
  .shell:not(.has-subnav) .sidebar{position:fixed;top:60px;left:0;bottom:0;width:250px;z-index:38;
    transform:translateX(-100%);transition:transform .2s ease;box-shadow:var(--shadow-lg);}
  .shell:not(.has-subnav) .sidebar.open{transform:translateX(0);}
  .content{padding:26px 24px 70px;}
  .search-wrap{max-width:260px;}
  .tool-grid,.benefits{grid-template-columns:repeat(2,1fr);}
  .hero-title{font-size:40px;}
  .home-section{padding:36px 22px 18px;}
}

/* ---- 760px: lesson list becomes a horizontal strip above the content ---- */
@media (max-width:760px){
  .shell.has-subnav{grid-template-rows:60px auto 1fr;grid-template-columns:1fr;
    grid-template-areas:"header" "subnav" "main";}
  .subnav{position:static;height:auto;width:auto;border-right:none;
    border-bottom:1px solid var(--border);padding:10px 14px;
    display:flex;gap:8px;overflow-x:auto;overflow-y:hidden;
    -webkit-overflow-scrolling:touch;}
  .subnav-head{display:none;}
  .subnav-track{display:flex;gap:8px;margin:0;align-items:center;}
  .subnav-track-label{padding:0 4px 0 0;white-space:nowrap;align-self:center;}
  .subnav-item{white-space:nowrap;margin:0;padding:7px 11px;border:1px solid var(--border);
    border-radius:20px;background:var(--glass);}
  .subnav-item::before{display:none;}
  .subnav-item.active{border-color:var(--tool);}
  .subnav-label{max-width:none;}
  .subnav-min{display:none;}
  .search-wrap{display:none;}
  .content{padding:22px 18px 60px;}
  .tool-grid,.benefits{grid-template-columns:1fr;}
  .home-nav{display:none;}
}

/* ---- 640px: chrome tightening ---- */
@media (max-width:760px){
  .home-header{gap:10px;padding:0 16px;}
  .home-nav{display:none;}
  .tool-grid,.benefits,.idx-grid{grid-template-columns:1fr;}
  .header-cta{padding:8px 13px;font-size:12.5px;}
}
@media (max-width:640px){
  .topbar{gap:9px;padding:0 12px;}
  .topbar .divider-v{display:none;}
  .tool-switch-btn{padding:6px 9px 6px 7px;gap:7px;}
  .tool-switch-btn .id{display:none;}
  .tool-menu{width:min(280px,calc(100vw - 24px));}
  .home-header{gap:9px;padding:0 14px;}
  .home-nav{display:none;}
  .hero{padding:18px 18px 26px;}
  .hero-title{font-size:32px;}
  .hero-sub{font-size:15px;}
  .home-section{padding:32px 18px 16px;}
  .tool-grid,.benefits{grid-template-columns:1fr;}
  .q-title,.page-head h1{font-size:23px;}
  .gloss-row{grid-template-columns:1fr;gap:5px;}
  .lesson-row{flex-direction:column;align-items:flex-start;gap:9px;}
  .lr-meta{align-self:flex-start;}
  .q-footer{flex-direction:column;align-items:stretch;gap:10px;}
  .nav-link,.nav-link.next{max-width:100%;margin-left:0;text-align:left;}
}

/* ---- 430px: drop the least essential chrome ---- */
@media (max-width:430px){
  .brand{font-size:0;gap:0;}
  .brand .brand-mark{font-size:11.5px;}
  .header-cta{display:none;}
  .hero-title{font-size:27px;}
}

/* ---------- document viewer ---------- */
/* Document pages drop the reading-width cap so the viewer can use the room. */
.content.wide{max-width:none;padding:20px 26px 60px;}

.doc-top{display:flex;align-items:center;justify-content:space-between;gap:16px;
  flex-wrap:wrap;margin-bottom:12px;}
.doc-titles{min-width:0;}
.doc-crumb{font-family:var(--font-mono);font-size:11.5px;color:var(--text-3);
  display:flex;align-items:center;gap:6px;margin-bottom:5px;flex-wrap:wrap;}
.doc-crumb a:hover{color:var(--text-2);}
.doc-crumb .sep{color:var(--border-strong);}
.doc-title{font-family:var(--font-display);font-weight:600;font-size:21px;
  line-height:1.25;margin:0;overflow-wrap:break-word;}
.doc-tools{display:flex;align-items:center;gap:8px;flex-shrink:0;}
.doc-chip{font-family:var(--font-mono);font-size:10.5px;color:var(--tool);
  background:rgba(45,217,201,.1);border:1px solid rgba(45,217,201,.22);
  border-radius:20px;padding:4px 11px;white-space:nowrap;}
.doc-btn{display:flex;align-items:center;gap:7px;font-size:12.5px;font-weight:600;
  padding:8px 14px;border-radius:9px;background:var(--glass);
  border:1px solid var(--border);color:var(--text-2);}
.doc-btn:hover{color:var(--text);border-color:var(--border-strong);}

.doc-viewer{position:relative;border:1px solid var(--border);border-radius:var(--r-lg);
  overflow:hidden;background:var(--bg-2);margin-bottom:26px;}
.doc-frame{width:100%;height:calc(100vh - 190px);min-height:520px;display:block;border:0;}

/* lazy poster: the PDF is not fetched until the reader asks for it */
.doc-poster{height:calc(100vh - 190px);min-height:520px;display:flex;
  flex-direction:column;align-items:center;justify-content:center;gap:14px;
  text-align:center;padding:32px;cursor:pointer;
  background:radial-gradient(120% 90% at 50% 0%,rgba(124,147,255,.08),transparent 60%);}
.doc-poster:hover{background:radial-gradient(120% 90% at 50% 0%,rgba(124,147,255,.13),transparent 60%);}
.doc-poster-icon{width:54px;height:54px;border-radius:15px;background:var(--glass);
  border:1px solid var(--border);display:flex;align-items:center;justify-content:center;
  color:var(--text-2);}
.doc-poster h2{font-family:var(--font-display);font-weight:600;font-size:18px;margin:2px 0 0;}
.doc-poster p{margin:0;font-size:13.5px;line-height:1.6;color:var(--text-3);max-width:44ch;}
.doc-poster .btn-primary{margin-top:6px;}
.doc-size{font-family:var(--font-mono);font-size:11px;color:var(--text-3);}
.doc-spinner{width:26px;height:26px;border-radius:50%;border:2px solid var(--border);
  border-top-color:var(--accent-b);animation:spin .8s linear infinite;}
@keyframes spin{to{transform:rotate(360deg);}}
@media (max-width:900px){ .doc-poster{height:calc(100vh - 230px);min-height:440px;} }
.doc-viewer.full{position:fixed;inset:0;z-index:90;border-radius:0;margin:0;border:none;}
.doc-viewer.full .doc-frame{height:100vh;min-height:0;}
.doc-exit{display:none;position:absolute;top:14px;right:16px;z-index:2;
  align-items:center;gap:7px;font-size:12.5px;font-weight:600;padding:9px 15px;
  border-radius:9px;background:rgba(10,12,18,.86);border:1px solid var(--border-strong);
  color:#F3F4F7;backdrop-filter:blur(8px);}
.doc-viewer.full .doc-exit{display:flex;}
.doc-fallback{padding:56px 28px;text-align:center;display:flex;flex-direction:column;
  align-items:center;gap:12px;}
.doc-fallback h2{font-family:var(--font-display);font-weight:600;font-size:17px;margin:4px 0 0;}
.doc-fallback p{margin:0;font-size:13.5px;line-height:1.6;color:var(--text-3);max-width:46ch;}

/* prose sits BELOW the document, not above it */
.doc-below{display:grid;grid-template-columns:minmax(0,1.6fr) minmax(0,1fr);
  gap:32px;align-items:start;}
.doc-about-label{font-family:var(--font-mono);font-size:10.5px;letter-spacing:.06em;
  text-transform:uppercase;color:var(--tool);margin-bottom:9px;
  display:flex;align-items:center;gap:8px;}
.doc-about-label::after{content:'';flex:1;height:1px;background:var(--border);}
.doc-about p{margin:0;font-size:14.5px;line-height:1.7;color:var(--text-2);}
@media (max-width:900px){
  .doc-below{grid-template-columns:1fr;gap:24px;}
  .doc-frame{height:calc(100vh - 230px);min-height:440px;}
}

/* outline lessons in the subnav read as not-yet-written */
.subnav-item.outline .subnav-label{color:var(--text-3);}
.subnav-item.outline:hover .subnav-label{color:var(--text-2);}
.subnav-item.outline .subnav-num{opacity:.55;}

/* outline lesson page state */
.outline-note{background:var(--glass);border:1px solid var(--border);
  border-left:2px solid var(--warn);border-radius:0 var(--r-md) var(--r-md) 0;
  padding:18px 22px;margin-bottom:28px;}
.outline-note-label{font-family:var(--font-mono);font-size:10.5px;letter-spacing:.06em;
  text-transform:uppercase;color:var(--warn);margin-bottom:8px;}
.outline-note p{margin:0 0 10px;font-size:14.5px;line-height:1.65;color:var(--text-2);}
.outline-note p:last-child{margin-bottom:0;}

/* ---------- flashcard study mode ---------- */
.deck-modes{display:flex;gap:8px;margin-bottom:18px;}
.deck-mode{font-size:13px;font-weight:500;padding:8px 15px;border-radius:9px;
  background:var(--glass);border:1px solid var(--border);color:var(--text-2);}
.deck-mode:hover{color:var(--text);border-color:var(--border-strong);}
.deck-mode.on{background:linear-gradient(135deg,rgba(124,147,255,.16),rgba(45,217,201,.16));
  color:var(--text);border-color:var(--border-strong);}

.study{margin-bottom:28px;}
.study-card{position:relative;min-height:300px;border-radius:var(--r-xl);
  border:1px solid var(--border);background:var(--glass);padding:38px 34px;
  display:flex;flex-direction:column;justify-content:center;gap:16px;cursor:pointer;
  text-align:center;transition:border-color .15s,background .15s;}
.study-card:hover{border-color:var(--border-strong);background:var(--glass-hover);}
.study-side{font-family:var(--font-mono);font-size:10px;letter-spacing:.07em;
  text-transform:uppercase;color:var(--text-3);}
.study-q{font-family:var(--font-display);font-weight:600;font-size:22px;line-height:1.35;}
.study-a{font-size:15.5px;line-height:1.75;color:var(--text-2);text-align:left;
  max-width:64ch;margin:0 auto;}
.study-hint{font-family:var(--font-mono);font-size:10.5px;color:var(--text-3);margin-top:6px;}
.study-bar{display:flex;align-items:center;gap:12px;margin-top:14px;flex-wrap:wrap;}
.study-btn{display:flex;align-items:center;gap:7px;font-size:13.5px;font-weight:600;
  padding:10px 18px;border-radius:10px;background:var(--glass);
  border:1px solid var(--border);color:var(--text-2);}
.study-btn:hover:not(:disabled){color:var(--text);border-color:var(--border-strong);}
.study-btn:disabled{opacity:.35;cursor:not-allowed;}
.study-btn.primary{background:var(--grad);color:var(--on-grad);border-color:transparent;}
.study-btn.primary:hover{filter:brightness(1.08);}
.study-count{font-family:var(--font-mono);font-size:12.5px;color:var(--text-3);margin-left:auto;}
.study-track{height:4px;border-radius:4px;background:var(--glass);overflow:hidden;margin-top:12px;}
.study-fill{height:100%;background:var(--grad);border-radius:4px;transition:width .2s;}

/* grid mode */
.deck-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:14px;}
.deck-card{position:relative;min-height:160px;border-radius:var(--r-lg);cursor:pointer;
  border:1px solid var(--border);background:var(--glass);padding:20px;text-align:left;
  display:flex;flex-direction:column;gap:10px;transition:border-color .15s,background .15s,transform .15s;}
.deck-card:hover{border-color:var(--border-strong);background:var(--glass-hover);transform:translateY(-2px);}
.deck-card.flipped{border-color:var(--tool);}
.deck-side{font-family:var(--font-mono);font-size:9.5px;letter-spacing:.06em;
  text-transform:uppercase;color:var(--text-3);}
.deck-front{font-size:14.5px;font-weight:500;line-height:1.5;color:var(--text);}
.deck-back{font-size:13.5px;line-height:1.65;color:var(--text-2);display:none;}
.deck-card.flipped .deck-front{display:none;}
.deck-card.flipped .deck-back{display:block;}
.deck-hint{font-family:var(--font-mono);font-size:9.5px;color:var(--text-3);margin-top:auto;}
.deck-link{font-size:12px;color:var(--tool);}
@media (max-width:640px){ .study-card{padding:28px 20px;min-height:260px;} .study-q{font-size:19px;} }

/* ---------- pdf.js viewer ---------- */
.pdfv{display:flex;flex-direction:column;height:100%;}
.pdfv-bar{display:flex;align-items:center;gap:7px;padding:9px 12px;flex-wrap:wrap;
  border-bottom:1px solid var(--border);background:var(--bg-1);}
.pdfv-btn{display:flex;align-items:center;justify-content:center;min-width:30px;height:30px;
  padding:0 9px;border-radius:8px;background:var(--glass);border:1px solid var(--border);
  color:var(--text-2);font-size:13px;font-weight:600;line-height:1;}
.pdfv-btn:hover{color:var(--text);border-color:var(--border-strong);}
.pdfv-page{font-family:var(--font-mono);font-size:12px;color:var(--text-3);
  display:flex;align-items:center;gap:5px;}
.pdfv-page input{width:44px;height:30px;text-align:center;border-radius:8px;
  background:var(--bg-2);border:1px solid var(--border);color:var(--text);
  font-family:var(--font-mono);font-size:12px;}
.pdfv-page input:focus{outline:none;border-color:var(--accent-a);}
.pdfv-sep{width:1px;height:20px;background:var(--border);margin:0 3px;}
.pdfv-zoom{font-family:var(--font-mono);font-size:11.5px;color:var(--text-3);min-width:42px;text-align:center;}
.pdfv-stage{flex:1;overflow:auto;display:flex;justify-content:center;
  padding:18px;background:var(--bg-3);}
.pdfv-stage canvas{max-width:100%;height:auto;border-radius:4px;
  box-shadow:0 6px 22px rgba(0,0,0,.35);align-self:flex-start;}
html[data-theme="light"] .pdfv-stage{background:#EDEFF4;}
html[data-theme="light"] .pdfv-stage canvas{box-shadow:0 6px 20px rgba(16,20,32,.16);}
#docMount{height:calc(100vh - 190px);min-height:520px;}
.doc-viewer.full #docMount{height:100vh;min-height:0;}
@media (max-width:900px){
  #docMount{height:calc(100vh - 230px);min-height:440px;}
  .pdfv-bar{gap:5px;padding:8px;}
  .pdfv-btn#pv-fit{display:none;}
}