/* ============ Shared design system — Term 1 Study Site ============ */
:root{
  --ink:#1F2430; --ink-soft:#5D6577; --paper:#FFFBF3; --line:#EDE3CC;
  --sun:#FFB921; --sun-tint:#FFF3D6;
  --sky:#3E6BF0; --sky-tint:#E8EEFF;
  --leaf:#28A26B; --leaf-tint:#E2F7EC;
  --berry:#E14F6B; --berry-tint:#FDE8EC;
  --grape:#8C5CF0; --grape-tint:#F2ECFE;
  --card:#FFFFFF;
}
html[data-theme="dark"]{
  --ink:#F2EFE6; --ink-soft:#B7BECF; --paper:#171A22; --line:#33384A;
  --sun-tint:#3A2E10; --sky-tint:#1B2440; --leaf-tint:#12291F; --berry-tint:#301820; --grape-tint:#26193E;
  --card:#1E2230;
}
@media (prefers-color-scheme: dark){
  html:not([data-theme="light"]):not([data-theme="dark"]){
    --ink:#F2EFE6; --ink-soft:#B7BECF; --paper:#171A22; --line:#33384A;
    --sun-tint:#3A2E10; --sky-tint:#1B2440; --leaf-tint:#12291F; --berry-tint:#301820; --grape-tint:#26193E;
    --card:#1E2230;
  }
}
*{box-sizing:border-box}
html,body{margin:0}
html{overflow-x:hidden}
body{background:var(--paper);color:var(--ink);
  font-family:'Nunito',system-ui,-apple-system,sans-serif;
  font-size:17px;line-height:1.65;-webkit-font-smoothing:antialiased;
  overflow-x:hidden;max-width:100vw}
img,svg{max-width:100%}
h1,h2,h3,h4{font-family:'Baloo 2',system-ui,sans-serif;font-weight:700;text-wrap:balance;margin:0}
a{color:inherit}

/* ---- top nav (every page) ---- */
.topnav{position:sticky;top:0;z-index:40;background:var(--paper);border-bottom:2px solid var(--line);
  display:flex;align-items:center;justify-content:space-between;gap:14px;
  padding:12px 20px;font-family:'Baloo 2',sans-serif;font-weight:700;font-size:14.5px}
.topnav .crumb{display:flex;align-items:center;gap:8px;flex-wrap:wrap;color:var(--ink-soft);min-width:0}
.topnav .crumb a{text-decoration:none;color:var(--ink-soft);white-space:nowrap}
.topnav .crumb a:hover{color:var(--sky)}
.topnav .crumb .sep{opacity:.5}
.topnav .crumb .here{color:var(--ink)}
.topnav .actions{display:flex;align-items:center;gap:8px;flex:none}
.iconbtn{background:var(--sky-tint);color:var(--sky);border:none;border-radius:10px;
  width:38px;height:38px;font-size:17px;cursor:pointer;display:flex;align-items:center;
  justify-content:center;transition:.15s}
.iconbtn:hover{background:#d8e2ff}
.navlink{background:var(--sky);color:#fff;border-radius:10px;padding:8px 14px;
  text-decoration:none;font-size:13.5px;display:flex;align-items:center;gap:6px;white-space:nowrap}
.navlink:hover{background:#2f56cc}
.navlink.ghost{background:var(--sky-tint);color:var(--sky)}
.navlink.ghost:hover{background:#d8e2ff}

/* ---- layout ---- */
.wrap{display:grid;grid-template-columns:220px minmax(0,740px);gap:36px;
  max-width:1040px;margin:0 auto;padding:32px 20px 100px}
.wrap main{min-width:0}
@media (max-width:840px){.wrap{grid-template-columns:minmax(0,1fr)}.toc{display:none}}

/* ---- sidebar / TOC (desktop/tablet ≥841px) ---- */
.toc{position:sticky;top:78px;align-self:start;font-size:14.5px;max-height:calc(100vh - 100px);overflow-y:auto}
.toc .who{font-family:'Baloo 2',sans-serif;font-weight:700;font-size:13px;
  color:var(--sky);text-transform:uppercase;letter-spacing:.5px;margin-bottom:6px}
.toc .progress{background:var(--sky-tint);border-radius:10px;height:8px;margin:10px 0 18px;overflow:hidden}
.toc .progress-bar{background:linear-gradient(90deg,var(--sky),var(--grape));height:100%;width:0%;
  border-radius:10px;transition:width .4s ease}
.toc a{display:flex;align-items:center;gap:8px;color:var(--ink-soft);text-decoration:none;
  padding:8px 10px;border-radius:10px;font-size:14px;font-weight:700;transition:.15s}
.toc a:hover, .toc a:focus-visible{background:var(--sky-tint);color:var(--sky)}
.toc a.active{background:var(--sky);color:#fff}
.toc a .num{width:22px;height:22px;border-radius:50%;background:var(--sky-tint);color:var(--sky);
  font-size:12px;display:flex;align-items:center;justify-content:center;flex:none;font-family:'Baloo 2',sans-serif}
.toc a.active .num{background:rgba(255,255,255,.25);color:#fff}
.toc .back{display:block;margin-top:20px;font-size:12.5px;color:var(--ink-soft)}

/* ---- mobile TOC (≤840px): sticky bar that expands into a dropdown list ---- */
.toc-mobile{display:none}
@media (max-width:840px){
  .toc-mobile{display:block;position:sticky;top:56px;z-index:35;background:var(--paper);
    border-bottom:2px solid var(--line);margin:0 0 24px;padding:0}
  .toc-mobile .progress{background:var(--sky-tint);border-radius:10px;height:6px;margin:0;overflow:hidden}
  .toc-mobile .progress-bar{background:linear-gradient(90deg,var(--sky),var(--grape));height:100%;width:0%;
    border-radius:10px;transition:width .4s ease}
  .toc-mobile-btn{width:100%;display:flex;align-items:center;justify-content:space-between;gap:10px;
    background:none;border:none;padding:10px 0;font-family:'Baloo 2',sans-serif;font-weight:700;
    font-size:14.5px;color:var(--ink);cursor:pointer;text-align:left}
  .toc-mobile-btn .cur{display:flex;align-items:center;gap:8px;min-width:0;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
  .toc-mobile-btn .cur .num{width:20px;height:20px;border-radius:50%;background:var(--sky-tint);color:var(--sky);
    font-size:11px;display:flex;align-items:center;justify-content:center;flex:none;font-family:'Baloo 2',sans-serif}
  .toc-mobile-btn .chev{transition:transform .25s ease;flex:none;color:var(--ink-soft)}
  .toc-mobile.open .toc-mobile-btn .chev{transform:rotate(180deg)}
  .toc-mobile-list{max-height:0;overflow:hidden;transition:max-height .3s ease}
  .toc-mobile.open .toc-mobile-list{max-height:70vh;overflow-y:auto}
  .toc-mobile-list a{display:flex;align-items:center;gap:8px;color:var(--ink-soft);text-decoration:none;
    padding:10px 4px;font-size:14.5px;font-weight:700;border-top:1px solid var(--line);min-width:0}
  .toc-mobile-list a span:not(.num){min-width:0;overflow-wrap:break-word}
  .toc-mobile-list a.active{color:var(--sky)}
  .toc-mobile-list a .num{width:20px;height:20px;border-radius:50%;background:var(--sky-tint);color:var(--sky);
    font-size:11px;display:flex;align-items:center;justify-content:center;flex:none;font-family:'Baloo 2',sans-serif}
  .toc-mobile-list a.active .num{background:var(--sky);color:#fff}
}

/* ---- mascot + speech ---- */
.mascot{width:44px;height:44px;flex:none}
.say{display:flex;gap:14px;align-items:flex-start;margin:22px 0;max-width:68ch}
.say .bubble{background:var(--card);border:2px solid var(--line);border-radius:18px 18px 18px 4px;
  padding:14px 18px;font-size:16px;position:relative;flex:1;min-width:0}
.say .bubble b{color:var(--sky)}

/* ---- hero ---- */
.hero{padding:30px 0 26px;margin-bottom:6px;position:relative}
.hero .eyebrow{display:inline-flex;align-items:center;gap:8px;font-family:'Baloo 2',sans-serif;
  font-weight:700;font-size:13.5px;color:var(--sky);background:var(--sky-tint);
  padding:5px 14px;border-radius:20px;letter-spacing:.3px;margin-bottom:16px}
.hero h1{font-size:40px;letter-spacing:.2px;line-height:1.08}
.hero p{color:var(--ink-soft);font-size:17px;margin-top:14px;max-width:58ch;font-weight:600}

/* ---- sections ---- */
section{margin-top:64px;scroll-margin-top:78px}
.sec-head{display:flex;align-items:center;gap:12px;margin-bottom:6px}
.sec-head .badge{width:38px;height:38px;border-radius:12px;display:flex;align-items:center;
  justify-content:center;font-family:'Baloo 2',sans-serif;font-weight:800;font-size:17px;color:#fff;flex:none}
section h2{font-size:27px}
section h3{font-size:19px;margin:28px 0 8px;color:var(--ink)}
p{margin:12px 0;max-width:66ch}
ul,ol{margin:10px 0;padding-left:22px;max-width:64ch}
li{margin:6px 0}
strong{color:var(--ink)}

/* ---- fact table ---- */
.tw{overflow-x:auto;margin:18px 0;border-radius:16px;border:2px solid var(--line)}
table{width:100%;border-collapse:collapse;font-size:15px}
th{background:var(--sky-tint);color:var(--sky);text-align:left;
  font-family:'Baloo 2',sans-serif;font-weight:700;font-size:13.5px;padding:11px 14px}
td{padding:11px 14px;border-top:1px solid var(--line);vertical-align:top}
tr:first-child td{border-top:none}
td.n{width:30px;text-align:right;color:var(--ink-soft);font-variant-numeric:tabular-nums;font-weight:800}

/* ---- boxes ---- */
.box{border-radius:16px;padding:18px 22px;margin:20px 0;font-size:15.5px;max-width:64ch;border:2px solid transparent}
.box p:first-child{margin-top:0} .box p:last-child{margin-bottom:0}
.explain{background:var(--sky-tint);border-color:#c7d6ff}
.explain .bt{color:var(--sky)}
.trick{background:var(--leaf-tint);border-color:#bfe9d3}
.trick .bt{color:var(--leaf)}
.warn{background:var(--berry-tint);border-color:#f6c9d2}
.warn .bt{color:var(--berry)}
.bt{font-family:'Baloo 2',sans-serif;font-weight:700;font-size:15.5px;display:flex;align-items:center;gap:8px;margin-bottom:8px}

/* ---- click to reveal ---- */
.reveal{margin:22px 0;max-width:64ch}
.reveal-btn{width:100%;text-align:left;background:var(--card);border:2px dashed var(--sky);
  border-radius:16px;padding:16px 20px;font-family:'Nunito',sans-serif;font-size:16px;font-weight:800;
  color:var(--sky);cursor:pointer;display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;
  gap:8px 12px;transition:.15s;overflow-wrap:break-word;word-break:break-word}
.reveal-btn:hover{background:var(--sky-tint)}
.reveal-btn .hint{font-weight:700;font-size:13px;color:var(--ink-soft);background:var(--paper);padding:4px 12px;border-radius:20px;flex:none}
.reveal-body{max-height:0;overflow:hidden;transition:max-height .4s ease}
.reveal.open .reveal-body{max-height:1200px}
.reveal.open .reveal-btn{border-style:solid;border-radius:16px 16px 0 0}
.reveal-inner{background:var(--card);border:2px solid var(--sky);border-top:none;border-radius:0 0 16px 16px;padding:18px 20px}
.reveal.open .reveal-btn .chev{transform:rotate(180deg)}
.chev{transition:transform .3s ease;flex:none}
.pop{display:inline-block}
.reveal.open .pop{animation:pop .45s cubic-bezier(.34,1.56,.64,1)}
@keyframes pop{0%{transform:scale(.85);opacity:0}60%{transform:scale(1.06)}100%{transform:scale(1);opacity:1}}
@media (prefers-reduced-motion:reduce){.reveal.open .pop{animation:none}.reveal-body{transition:none}}

/* ---- worked example card ---- */
.eg{background:var(--card);border:2px solid var(--line);border-radius:18px;overflow:hidden;margin:24px 0;max-width:64ch}
.eg-h{background:var(--grape);color:#fff;padding:11px 20px;font-family:'Baloo 2',sans-serif;font-weight:700;font-size:15.5px;display:flex;flex-wrap:wrap;align-items:center;gap:8px}
.eg-body{padding:18px 20px}
.step{display:grid;grid-template-columns:26px 1fr;gap:0 10px;margin:10px 0}
.step .sn{width:24px;height:24px;border-radius:50%;background:var(--grape-tint);color:var(--grape);font-weight:800;font-size:12.5px;display:flex;align-items:center;justify-content:center;margin-top:2px;font-family:'Baloo 2',sans-serif}
.eg-ans{background:var(--grape-tint);border-top:2px solid var(--grape);padding:12px 20px;font-weight:800;color:var(--grape)}

/* ---- math notation ---- */
.math{font-family:'Consolas','DejaVu Sans Mono',monospace;font-size:.92em;background:var(--sky-tint);padding:2px 7px;border-radius:6px;display:inline-block;font-variant-numeric:tabular-nums;font-weight:700;color:var(--sky)}
.mathblock{font-family:'Consolas','DejaVu Sans Mono',monospace;font-size:14.5px;background:var(--ink);color:#EAF0FF;padding:14px 18px;border-radius:12px;margin:14px 0;white-space:pre-wrap;line-height:1.85;overflow-x:auto;max-width:64ch}
html[data-theme="dark"] .mathblock{background:#0E1016}

/* ---- interactive dot builder ---- */
.builder{background:var(--card);border:2px solid var(--line);border-radius:18px;padding:22px;margin:22px 0;max-width:64ch}
.builder .stage{min-height:230px;display:flex;align-items:center;justify-content:center;padding:16px 0}
.builder .controls{display:flex;align-items:center;justify-content:center;gap:14px;margin-top:14px;flex-wrap:wrap}
.builder button{font-family:'Baloo 2',sans-serif;font-weight:700;font-size:15px;border:none;border-radius:12px;padding:10px 20px;cursor:pointer;transition:.15s}
.builder .step-btn{background:var(--sky);color:#fff}
.builder .step-btn:hover{background:#2f56cc}
.builder .step-btn:disabled{background:var(--line);color:var(--ink-soft);cursor:default}
.builder .reset-btn{background:var(--sky-tint);color:var(--sky)}
.builder .reset-btn:hover{background:#d8e2ff}
.builder .readout{text-align:center;margin-top:14px;font-family:'Baloo 2',sans-serif;font-size:16px;color:var(--ink)}
.builder .readout .eq{color:var(--berry);font-weight:800}
svg .dot{transition:opacity .35s ease}
svg .layer-in{animation:dotpop .4s cubic-bezier(.34,1.56,.64,1)}
@keyframes dotpop{0%{transform:scale(0)}70%{transform:scale(1.25)}100%{transform:scale(1)}}
@media (prefers-reduced-motion:reduce){svg .layer-in{animation:none}}

/* ---- chips ---- */
.chips{display:flex;flex-wrap:wrap;gap:9px;margin:16px 0}
.chip{background:var(--sky-tint);color:var(--sky);border-radius:20px;padding:7px 15px;font-size:13.5px;font-weight:800;font-family:'Baloo 2',sans-serif}
.chip.g{background:var(--leaf-tint);color:var(--leaf)}
.chip.p{background:var(--grape-tint);color:var(--grape)}
.chip.o{background:var(--sun-tint);color:#946200}

/* ---- prev/next footer nav ---- */
.chnav{display:flex;justify-content:space-between;gap:14px;margin-top:60px;padding-top:24px;border-top:2px solid var(--line)}
.chnav a{flex:1;max-width:48%;text-decoration:none;background:var(--card);border:2px solid var(--line);
  border-radius:14px;padding:14px 18px;transition:.15s}
.chnav a:hover{border-color:var(--sky)}
.chnav a.next{text-align:right;margin-left:auto}
.chnav .lbl{font-size:12px;color:var(--ink-soft);font-weight:700;text-transform:uppercase;letter-spacing:.4px}
.chnav .ttl{font-family:'Baloo 2',sans-serif;font-weight:700;color:var(--ink);margin-top:3px}

.done{margin-top:64px;padding-top:26px;border-top:2px solid var(--line);color:var(--ink-soft);font-size:14px;text-align:center;font-weight:700}

/* ---- flip flashcards ---- */
.fc-note{color:var(--ink-soft);font-size:15px;margin-top:6px;max-width:64ch}
.fc-groups{display:flex;flex-wrap:wrap;gap:9px;margin:16px 0 28px}
.fc-tab{background:var(--card);border:2px solid var(--line);border-radius:20px;padding:7px 16px;
  font-family:'Baloo 2',sans-serif;font-weight:700;font-size:13.5px;color:var(--ink-soft);
  cursor:pointer;transition:.15s}
.fc-tab:hover{border-color:var(--sky);color:var(--sky)}
.fc-tab.active{background:var(--sky);border-color:var(--sky);color:#fff}
.fcgrid{display:grid;grid-template-columns:repeat(auto-fill,minmax(210px,1fr));gap:14px;margin:8px 0 20px}
.fcard{perspective:1000px;min-height:150px;cursor:pointer}
.fcard-in{position:relative;width:100%;height:100%;min-height:150px;transition:transform .5s cubic-bezier(.4,.2,.2,1);
  transform-style:preserve-3d}
.fcard.flipped .fcard-in{transform:rotateY(180deg)}
.fcard-face{position:absolute;inset:0;backface-visibility:hidden;border-radius:16px;border:2px solid var(--line);
  background:var(--card);padding:16px 17px;display:flex;flex-direction:column;justify-content:center;gap:6px}
.fcard-face.front{}
.fcard-face .q{font-family:'Baloo 2',sans-serif;font-weight:700;font-size:15.5px;line-height:1.3;color:var(--ink)}
.fcard-face .hint{font-size:12px;font-style:italic;color:var(--ink-soft)}
.fcard-face .tap{position:absolute;bottom:10px;right:14px;font-size:11px;color:var(--ink-soft);font-weight:700}
.fcard-face.back{transform:rotateY(180deg);background:var(--sky-tint);border-color:var(--sky)}
.fcard-face.back .a{font-family:'Baloo 2',sans-serif;font-weight:800;font-size:16px;color:var(--sky);line-height:1.3}
@media (prefers-reduced-motion:reduce){.fcard-in{transition:none}}

/* ============ Hub / landing pages ============ */
.hub{max-width:1040px;margin:0 auto;padding:48px 20px 100px}
.hub-hero{text-align:center;padding:40px 0 44px}
.hub-hero h1{font-size:44px;line-height:1.1}
.hub-hero p{color:var(--ink-soft);font-size:17.5px;font-weight:600;margin-top:12px;max-width:52ch;margin-left:auto;margin-right:auto}
.pickgrid{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));gap:20px;margin-top:28px}
.pickcard{display:block;text-decoration:none;background:var(--card);border:2.5px solid var(--line);
  border-radius:22px;padding:28px 24px;transition:.18s;position:relative;overflow:hidden}
.pickcard:hover{border-color:var(--sky);transform:translateY(-3px)}
.pickcard .icon{font-size:40px;margin-bottom:14px;display:block}
.pickcard h3{font-size:22px;color:var(--ink)}
.pickcard p{color:var(--ink-soft);font-size:14.5px;font-weight:600;margin:8px 0 0}
.pickcard .count{display:inline-flex;align-items:center;gap:6px;margin-top:14px;font-size:12.5px;
  font-weight:800;font-family:'Baloo 2',sans-serif;color:var(--sky);background:var(--sky-tint);
  padding:4px 12px;border-radius:20px}

.crumbbar{max-width:1040px;margin:0 auto;padding:20px 20px 0;font-size:14px;font-weight:700;color:var(--ink-soft)}
.crumbbar a{text-decoration:none;color:var(--ink-soft)}
.crumbbar a:hover{color:var(--sky)}

.chlist{display:flex;flex-direction:column;gap:12px;margin-top:24px}
.chrow{display:flex;align-items:center;gap:16px;background:var(--card);border:2px solid var(--line);
  border-radius:16px;padding:16px 20px;text-decoration:none;transition:.15s}
.chrow:hover{border-color:var(--sky)}
.chrow .cnum{width:40px;height:40px;border-radius:12px;background:var(--sky-tint);color:var(--sky);
  font-family:'Baloo 2',sans-serif;font-weight:800;font-size:16px;display:flex;align-items:center;justify-content:center;flex:none}
.chrow .cbody{flex:1;min-width:0}
.chrow .ctitle{font-family:'Baloo 2',sans-serif;font-weight:700;font-size:16.5px;color:var(--ink)}
.chrow .csub{font-size:13px;color:var(--ink-soft);margin-top:2px}
.chrow .cstatus{flex:none;font-size:12px;font-weight:800;font-family:'Baloo 2',sans-serif;
  padding:5px 12px;border-radius:20px}
.chrow.ready{}
.chrow.ready .cstatus{background:var(--leaf-tint);color:var(--leaf)}
.chrow.soon{opacity:.55;cursor:default;pointer-events:none}
.chrow.soon .cstatus{background:var(--line);color:var(--ink-soft)}

@media (max-width:600px){
  body{font-size:16px}
  .hero h1{font-size:28px}
  .hub-hero h1{font-size:28px}
  .topnav{flex-wrap:wrap}
  .topnav .crumb{flex-wrap:wrap;white-space:normal}
  .topnav .crumb a, .topnav .crumb .here{white-space:normal}
  section h2{font-size:22px}
  .chnav{flex-direction:column}
  .chnav a{max-width:100%}
  .chnav a.next{text-align:left;margin-left:0}
  .fcgrid{grid-template-columns:repeat(auto-fill,minmax(150px,1fr))}
  .pickgrid{grid-template-columns:1fr}
}