/* ===== Data Visualization Study App ===== */
:root{
  --bg:#0b1622; --bg2:#0f1f2e; --panel:#13283b; --panel2:#16304a;
  --ink:#e7f0f7; --muted:#9bb8cc; --line:#23425e;
  --accent:#3a86ff; --accent2:#06d6a0; --gold:#ffd166; --pink:#ef476f;
  --radius:14px; --shadow:0 8px 28px rgba(0,0,0,.35);
}
*{box-sizing:border-box}
html,body{margin:0;height:100%}
body{
  background:radial-gradient(1200px 600px at 80% -10%,#1a3550 0,var(--bg) 55%);
  color:var(--ink); font:15px/1.55 -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  display:flex; min-height:100vh;
}
a{color:var(--accent); text-decoration:none}

/* ---- sidebar ---- */
.sidebar{
  width:230px; flex:0 0 230px; background:linear-gradient(180deg,var(--bg2),#0a1825);
  border-right:1px solid var(--line); padding:18px 12px; position:sticky; top:0; height:100vh; overflow-y:auto;
}
.brand{display:flex;align-items:center;gap:10px;padding:6px 8px 16px;border-bottom:1px solid var(--line);margin-bottom:12px}
.brand .logo{width:34px;height:34px;border-radius:9px;background:linear-gradient(135deg,var(--accent),var(--accent2));display:grid;place-items:center;font-weight:800;color:#03121d}
.brand b{font-size:15px;letter-spacing:.3px}
.brand small{display:block;color:var(--muted);font-size:11px}
#nav{display:flex;flex-direction:column;gap:3px}
#nav a{color:var(--muted);padding:9px 12px;border-radius:10px;font-weight:600;font-size:14px;display:flex;align-items:center}
#nav a:hover{background:var(--panel);color:var(--ink)}
#nav a.active{background:linear-gradient(135deg,rgba(58,134,255,.22),rgba(6,214,160,.16));color:#fff;box-shadow:inset 0 0 0 1px var(--line)}
.side-foot{margin-top:16px;padding:10px 8px;color:var(--muted);font-size:11px;border-top:1px solid var(--line)}

/* ---- main ---- */
main{flex:1;min-width:0;padding:30px 38px 80px;max-width:1080px}
h1{font-size:30px;margin:0 0 6px;letter-spacing:-.4px}
h2{font-size:21px;margin:30px 0 12px}
h3{margin:0 0 6px}
.sub{color:var(--muted);font-size:15px;margin:0 0 8px}
.badge{display:inline-block;background:var(--panel2);color:var(--gold);font-size:11px;font-weight:700;padding:3px 9px;border-radius:20px;letter-spacing:.5px;margin-bottom:8px}
.section-title{border-left:3px solid var(--accent);padding-left:10px}

/* hero */
.hero{padding:26px 28px;border-radius:var(--radius);background:linear-gradient(120deg,#13283b,#0f2236);box-shadow:var(--shadow);border:1px solid var(--line);margin-bottom:24px}
.hero h1{background:linear-gradient(90deg,#fff,#9fd6ff);-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent}

/* cards */
.card{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:16px 18px;box-shadow:var(--shadow)}
.grid{display:grid;gap:16px}
.cards-grid{grid-template-columns:repeat(auto-fit,minmax(230px,1fr))}
.lecture-card{transition:transform .15s,border-color .15s;position:relative}
.lecture-card:hover{transform:translateY(-3px);border-color:var(--accent)}
.lecture-card h3{font-size:17px}
.lecture-card p{color:var(--muted);font-size:13px;margin:6px 0 10px}
.card-link{color:var(--accent2);font-weight:700;font-size:13px}
.steps{grid-template-columns:repeat(auto-fit,minmax(210px,1fr))}
.steps .card{position:relative;padding-top:34px}
.step-n{position:absolute;top:12px;left:14px;width:24px;height:24px;border-radius:50%;background:var(--accent);color:#03121d;font-weight:800;display:grid;place-items:center;font-size:13px}
.steps b{display:block;margin-bottom:4px}
.steps p{color:var(--muted);font-size:13px;margin:0}
.big-list{padding-left:22px}
.big-list li{margin:7px 0}

/* lecture page */
.page-head{margin-bottom:18px}
.lecture-jump{display:flex;flex-wrap:wrap;gap:6px;margin-top:12px}
.lecture-jump a{font-size:12px;background:var(--panel);border:1px solid var(--line);padding:5px 10px;border-radius:20px;color:var(--muted)}
.lecture-jump a:hover{color:var(--ink);border-color:var(--accent)}
.lec-section{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:18px 20px;margin-bottom:18px;box-shadow:var(--shadow);scroll-margin-top:20px}
.lec-section h2{margin-top:0;color:#cfe7ff}
ul.pts{margin:0;padding-left:20px}
ul.pts li{margin:8px 0}
b{color:#fff}
.callout{margin-top:14px;padding:11px 14px;border-radius:10px;font-size:14px}
.callout.key{background:rgba(255,209,102,.12);border:1px solid rgba(255,209,102,.4)}
.callout.tip{background:rgba(6,214,160,.1);border:1px solid rgba(6,214,160,.35)}
.page-foot{margin-top:8px}

/* demos */
.demo-box{margin-top:16px;background:var(--bg2);border:1px dashed var(--line);border-radius:12px;padding:14px;position:relative}
.demo-tag{position:absolute;top:-10px;left:14px;background:var(--accent);color:#03121d;font-size:10px;font-weight:800;padding:2px 8px;border-radius:10px;letter-spacing:.5px}
.demo-note{color:var(--muted);font-size:12.5px;margin:10px 0 0;line-height:1.45}
.demo-controls{display:flex;flex-wrap:wrap;gap:10px;align-items:center;margin-bottom:12px}
.demo-controls label{color:var(--muted);font-size:13px;display:flex;align-items:center;gap:8px}
.demo-output{margin-top:10px;background:var(--panel2);border:1px solid var(--line);border-radius:9px;padding:10px 12px;font-size:13.5px;min-height:20px}
.preatt-grid{display:flex;flex-wrap:wrap;gap:2px 6px;font-family:ui-monospace,Menlo,monospace;font-size:15px;color:#cfe3f2;max-width:560px}
.preatt-grid span{width:14px;text-align:center}
.spark-row{display:flex;align-items:center;gap:8px;margin:6px 0;font-size:14px;color:var(--muted)}
.spark-tag{font-size:10px;font-weight:800;padding:2px 6px;border-radius:5px}
.spark-tag.good{background:rgba(6,214,160,.2);color:var(--accent2)}
.spark-tag.bad{background:rgba(239,71,111,.2);color:var(--pink)}

/* buttons / pills */
.btn{background:linear-gradient(135deg,var(--accent),#2f6fe0);color:#fff;border:none;padding:9px 16px;border-radius:10px;font-weight:700;font-size:14px;cursor:pointer;box-shadow:var(--shadow)}
.btn:hover{filter:brightness(1.08)}
.btn:disabled{opacity:.4;cursor:default;filter:none}
.btn-ghost{background:transparent;color:var(--muted);border:1px solid var(--line);box-shadow:none}
.btn-ghost:hover{color:var(--ink);border-color:var(--accent)}
.chip{font-size:13px;padding:6px 12px}
.pill{display:inline-block;background:var(--panel2);border:1px solid var(--line);color:#bfe0ff;border-radius:20px;padding:3px 10px;font-size:12.5px;margin:2px}

/* lab */
.lab-grid{grid-template-columns:repeat(auto-fit,minmax(340px,1fr))}
.lab-card h3{font-size:16px;color:#cfe7ff}
.lab-sub{color:var(--muted);font-size:13px;margin:2px 0 0}

/* quiz */
.quiz-filters{display:flex;gap:8px;flex-wrap:wrap;align-items:center;margin-bottom:16px}
.shuffle-lbl{color:var(--muted);font-size:13px;display:flex;gap:6px;align-items:center;margin-left:6px}
.quiz-card .quiz-meta{display:flex;justify-content:space-between;color:var(--muted);font-size:13px;margin-bottom:8px}
.quiz-q{font-size:19px;margin:4px 0 16px}
.quiz-opts{display:flex;flex-direction:column;gap:9px}
.opt{text-align:left;background:var(--panel2);border:1px solid var(--line);color:var(--ink);padding:12px 14px;border-radius:10px;cursor:pointer;font-size:14.5px;transition:.12s}
.opt:hover:not(:disabled){border-color:var(--accent);background:#1b3651}
.opt.correct{background:rgba(6,214,160,.18);border-color:var(--accent2);color:#d6fff0}
.opt.wrong{background:rgba(239,71,111,.16);border-color:var(--pink);color:#ffd9e2}
.quiz-exp{margin-top:14px;font-size:14px;color:var(--muted);max-height:0;overflow:hidden;transition:.2s}
.quiz-exp.show{max-height:300px;padding:12px 14px;background:var(--bg2);border:1px solid var(--line);border-radius:10px}
.quiz-nav{margin-top:16px;text-align:right}
.quiz-done{text-align:center;padding:34px}
.quiz-done h2{font-size:34px}

/* flashcards */
.fc-stage{display:flex;flex-direction:column;align-items:center;margin-top:10px}
.flashcard{width:min(560px,92%);height:260px;perspective:1200px;cursor:pointer}
.fc-inner{position:relative;width:100%;height:100%;transition:transform .5s;transform-style:preserve-3d}
.flashcard.flipped .fc-inner{transform:rotateY(180deg)}
.fc-face{position:absolute;inset:0;backface-visibility:hidden;border-radius:18px;border:1px solid var(--line);display:flex;flex-direction:column;align-items:center;justify-content:center;padding:24px;text-align:center;box-shadow:var(--shadow)}
.fc-front{background:linear-gradient(135deg,#16304a,#0f2236)}
.fc-back{background:linear-gradient(135deg,#123a32,#0f2236);transform:rotateY(180deg)}
.fc-label{font-size:11px;letter-spacing:2px;color:var(--gold);font-weight:800;margin-bottom:14px}
.fc-text{font-size:24px;font-weight:700}
.fc-text.small{font-size:17px;font-weight:500;line-height:1.5;color:#dbeaf5}
.fc-hint{position:absolute;bottom:14px;font-size:11px;color:var(--muted)}
.fc-controls{display:flex;gap:10px;margin-top:18px}
.fc-count{margin-top:12px;color:var(--muted);font-size:13px}

/* exam */
.exam-list{display:flex;flex-direction:column;gap:10px}
.exam-item{padding:0;overflow:hidden}
.exam-q{padding:14px 18px;cursor:pointer;font-weight:600;display:flex;align-items:center;gap:8px}
.exam-toggle{margin-left:auto;color:var(--accent2);font-size:20px;font-weight:800}
.exam-a{max-height:0;overflow:hidden;transition:.25s;padding:0 18px;color:var(--muted);font-size:14px;line-height:1.6}
.exam-item.open .exam-a{max-height:420px;padding:0 18px 16px}

/* cheat */
.cheat-grid{display:grid;gap:16px;grid-template-columns:repeat(auto-fit,minmax(300px,1fr))}
.cheat h3{color:var(--gold);border-bottom:1px solid var(--line);padding-bottom:8px;margin-bottom:8px}
.cheat ul{margin:0;padding-left:18px}
.cheat li{margin:6px 0;font-size:13.5px}

/* ---- rich content blocks (notes style) ---- */
.blk-p{margin:9px 0}
.blk-note{color:var(--muted);font-size:12.5px;font-style:italic;margin:8px 0;border-left:2px solid var(--line);padding-left:10px}
.sec-n{color:var(--accent2);font-weight:800;margin-right:7px;font-variant-numeric:tabular-nums}

/* tables */
.table-wrap{overflow-x:auto;margin:12px 0;border-radius:10px;border:1px solid var(--line)}
table.dv-table{border-collapse:collapse;width:100%;font-size:13.5px}
.dv-table th{text-align:left;background:var(--panel2);color:#cfe7ff;padding:8px 11px;border-bottom:1px solid var(--line);font-weight:700;white-space:nowrap}
.dv-table td{padding:7px 11px;border-top:1px solid var(--line);vertical-align:top}
.dv-table td:first-child{font-weight:600;color:#dbeaf5;white-space:nowrap}
.dv-table tbody tr:nth-child(even){background:rgba(255,255,255,.025)}
.dv-table tbody tr:hover{background:rgba(58,134,255,.08)}

/* definition / callout boxes */
.defbox{margin:13px 0;border-radius:11px;padding:11px 15px;border:1px solid var(--line)}
.def-label{display:inline-block;font-size:10px;font-weight:800;letter-spacing:1px;text-transform:uppercase;padding:2px 9px;border-radius:10px;margin-bottom:7px}
.def-body{font-size:14px;line-height:1.55}
.defbox.def-def{background:rgba(58,134,255,.10);border-color:rgba(58,134,255,.4)}
.def-def .def-label{background:rgba(58,134,255,.25);color:#bcd9ff}
.defbox.def-key{background:rgba(255,209,102,.10);border-color:rgba(255,209,102,.4)}
.def-key .def-label{background:rgba(255,209,102,.22);color:#ffe09a}
.defbox.def-rule{background:rgba(6,214,160,.10);border-color:rgba(6,214,160,.35)}
.def-rule .def-label{background:rgba(6,214,160,.22);color:#9af2d6}
.defbox.def-ex{background:rgba(168,123,255,.10);border-color:rgba(168,123,255,.4)}
.def-ex .def-label{background:rgba(168,123,255,.22);color:#d6c6ff}
.defbox.def-formula{background:#0e1f30}
.def-formula .def-label{background:#23425e;color:#cfe7ff}
.def-formula .def-body{font-family:ui-monospace,Menlo,monospace;font-size:13.5px}
.defbox.def-summary{background:linear-gradient(120deg,rgba(58,134,255,.16),rgba(6,214,160,.10));border-color:var(--accent)}
.def-summary .def-label{background:var(--accent);color:#03121d}

/* code blocks */
.code-block{background:#0e1f30;border:1px solid var(--line);border-radius:8px;padding:12px 14px;overflow-x:auto;font-size:12.5px;line-height:1.5;margin:12px 0}

/* datatypes demo */
.dt-prompt{font-size:15px;margin-bottom:10px}
.dt-count{color:var(--muted);font-size:12px}
button.btn.correct{background:rgba(6,214,160,.25);border-color:var(--accent2);color:#d6fff0}
button.btn.wrong{background:rgba(239,71,111,.22);border-color:var(--pink);color:#ffd9e2}

/* two-button footer */
.page-foot{display:flex;gap:10px;flex-wrap:wrap;align-items:center}

/* famous-viz gallery */
.fv-stage{display:flex;flex-direction:column;gap:8px}
.fv-img{width:100%;max-height:360px;object-fit:contain;background:#fbf7ee;border-radius:8px;border:1px solid var(--line)}
.fv-cap{font-size:13px;color:var(--ink);background:var(--panel2);border:1px solid var(--line);border-radius:8px;padding:10px 12px;line-height:1.5}
.fv-thumbs{display:flex;gap:6px;flex-wrap:wrap;margin-top:8px}
.fv-thumb{width:66px;height:46px;object-fit:cover;border-radius:6px;border:2px solid transparent;cursor:pointer;opacity:.55;background:#fbf7ee;transition:.15s}
.fv-thumb:hover{opacity:1}
.fv-thumb.active{border-color:var(--accent);opacity:1}

/* figure (inline annotated image) */
.fig{margin:14px 0;border:1px solid var(--line);border-radius:10px;overflow:hidden;background:var(--bg2)}
.fig-img{display:block;width:100%;max-height:440px;object-fit:contain;background:#fbf7ee}
.fig-cap{font-size:12.5px;color:var(--muted);padding:9px 12px;line-height:1.5}
.fig-credit{color:#6f8aa0;font-style:italic}

/* visual variables grid */
.vv-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(122px,1fr));gap:8px}
.vv-card{background:#0e2030;border:1px solid var(--line);border-radius:8px;padding:6px 6px 2px}
.vv-h{font-size:11px;color:#cfe7ff;margin-bottom:2px;display:flex;justify-content:space-between;align-items:center;gap:4px}
.vv-tag{font-size:8px;padding:1px 5px;border-radius:8px;font-weight:700;letter-spacing:.5px}
.vv-tag.q{background:rgba(58,134,255,.25);color:#bcd9ff}
.vv-tag.c{background:rgba(255,209,102,.22);color:#ffe09a}

/* colour-scale families */
.cs-row{margin:10px 0}
.cs-name{font-weight:700;color:#cfe7ff;font-size:13px;margin-bottom:3px}
.cs-use{font-size:12px;color:var(--muted);margin-top:3px;line-height:1.45}

/* svg text default */
svg text{font-family:inherit}

@media (max-width:760px){
  body{flex-direction:column}
  .sidebar{width:100%;height:auto;position:static;flex:none;display:flex;flex-direction:column}
  #nav{flex-direction:row;flex-wrap:wrap}
  main{padding:20px 16px 60px}
}
@media print{
  .sidebar{display:none}
  body{background:#fff;color:#000}
  .card,.cheat{break-inside:avoid;box-shadow:none;border:1px solid #ccc;background:#fff;color:#000}
  .cheat h3{color:#000}
  .btn{display:none}
}