:root{--b-econ:url("banners/econ.jpg");--b-ocm:url("banners/ocm.jpg");--b-sp:url("banners/sp.jpg");--b-bk:url("banners/bk.jpg")}
:root{--mascot:url("mascot.jpg")}
:root{
  --bg:#f3f6fb; --card:#ffffff; --text:#14213d; --muted:#586180; --line:#dfe5f2;
  --brand:#0b7a72; --on-brand:#ffffff; --brand-soft:#e2f4f2; --gold:#ffb627;
  --ok:#15803d; --ok-bg:#e3f5e9; --bad:#c2261f; --bad-bg:#fdeceb;
  --hero-a:#14213d; --hero-b:#0f6f69;
  --shadow:0 1px 2px rgba(20,33,61,.06),0 8px 24px rgba(20,33,61,.07);
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    --bg:#0b1222; --card:#141d33; --text:#eaf0ff; --muted:#9fabc9; --line:#25314f;
    --brand:#3ccfc2; --on-brand:#06201d; --brand-soft:#123033;
    --ok:#6fd08c; --ok-bg:#12301f; --bad:#ff8a80; --bad-bg:#3a1a1a;
    --hero-a:#101a33; --hero-b:#0d5a56; --shadow:0 8px 24px rgba(0,0,0,.35);
  }
}
:root[data-theme="dark"]{
  --bg:#0b1222; --card:#141d33; --text:#eaf0ff; --muted:#9fabc9; --line:#25314f;
  --brand:#3ccfc2; --on-brand:#06201d; --brand-soft:#123033;
  --ok:#6fd08c; --ok-bg:#12301f; --bad:#ff8a80; --bad-bg:#3a1a1a;
  --hero-a:#101a33; --hero-b:#0d5a56; --shadow:0 8px 24px rgba(0,0,0,.35);
}
*{box-sizing:border-box}
body{margin:0;font-family:Figtree,system-ui,-apple-system,Segoe UI,Roboto,sans-serif;background:var(--bg);color:var(--text);line-height:1.6}
h1,h2,h3,.brand{font-family:"Bricolage Grotesque",Figtree,system-ui,sans-serif}
h2,h3{text-wrap:balance}

/* header */
.top{display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:8px;padding:10px 20px;background:var(--card);border-bottom:1px solid var(--line);position:sticky;top:0;z-index:5}
.brand{display:flex;align-items:center;gap:10px;font-weight:800;font-size:1.15rem;color:var(--text);text-decoration:none}
.brand em{font-style:normal;color:var(--brand)}
.logo{flex:none;width:38px;height:38px;display:block}
.top-actions{display:flex;gap:6px}
button{font:inherit;cursor:pointer;border-radius:10px;border:1px solid var(--line);background:var(--card);color:var(--text);padding:8px 14px;transition:transform .12s,border-color .12s,background .12s}
button:hover{border-color:var(--brand)}
button:active{transform:scale(.98)}
button:focus-visible,select:focus-visible,input:focus-visible,li:focus-visible,textarea:focus-visible{outline:3px solid var(--brand);outline-offset:2px}
.tab.active,.primary{background:var(--brand);color:var(--on-brand);border-color:var(--brand);font-weight:600}
.icon{padding:8px 11px}

/* hero */
.hero{display:flex;align-items:center;justify-content:space-between;gap:24px;max-width:1100px;margin:16px auto 0;padding:28px 32px;border-radius:24px;color:#fff;background:linear-gradient(120deg,var(--hero-a),var(--hero-b));overflow:hidden;position:relative}
.hero-text{max-width:460px;position:relative;z-index:1}
.hero h1{font-size:clamp(1.7rem,4.5vw,2.6rem);line-height:1.1;margin:6px 0 10px;font-weight:800;text-wrap:balance}
.hero p{margin:0;color:#d5e3f0}
.eyebrow{text-transform:uppercase;letter-spacing:.12em;font-size:.75rem;font-weight:600;color:#ffb627!important}
.hero-art{width:min(420px,44%);height:auto;flex:none}

.layout{display:grid;grid-template-columns:300px 1fr;gap:20px;max-width:1100px;margin:20px auto;padding:0 16px}
.side,.card{background:var(--card);border:1px solid var(--line);border-radius:18px;padding:18px;box-shadow:var(--shadow)}
.side{align-self:start}
.cap{display:block;font-size:.72rem;text-transform:uppercase;letter-spacing:.1em;color:var(--muted);margin:16px 0 8px;font-family:Figtree,sans-serif;font-weight:600}

/* class switch */
.seg{display:grid;grid-template-columns:1fr 1fr;background:var(--bg);border-radius:12px;padding:4px;gap:4px}
.seg button{border:0;background:transparent;font-weight:600;color:var(--muted)}
.seg button.on{background:var(--card);color:var(--text);box-shadow:var(--shadow)}

/* subject tiles */
.subjects{display:grid;grid-template-columns:1fr 1fr;gap:8px}
.tile{display:flex;flex-direction:column;align-items:flex-start;gap:6px;text-align:left;padding:12px;border-radius:14px;line-height:1.25}
.tile b{font-size:.88rem}
.tile small{color:var(--muted);font-size:.74rem}
.tile.on{border-color:var(--sc);background:color-mix(in srgb,var(--sc) 12%,var(--card))}
.ico{display:grid;place-items:center;width:38px;height:38px;border-radius:11px;background:color-mix(in srgb,var(--sc) 18%,var(--card));color:var(--sc)}
.ico svg{width:22px;height:22px}

input[type=search]{width:100%;padding:10px 12px;border-radius:10px;border:1px solid var(--line);background:var(--bg);color:var(--text);font:inherit}
.chapters{list-style:none;margin:10px 0 0;padding:0;display:grid;gap:4px}
.chapters li{padding:9px 10px;border-radius:12px;cursor:pointer;display:flex;align-items:center;gap:10px}
.chapters li:hover{background:var(--bg)}
.chapters li.active{background:color-mix(in srgb,var(--sc,var(--brand)) 14%,var(--card));font-weight:600}
.num{flex:none;display:grid;place-items:center;width:26px;height:26px;border-radius:8px;background:var(--bg);font-size:.8rem;font-weight:600;font-variant-numeric:tabular-nums}
.chapters li.active .num{background:var(--sc,var(--brand));color:#fff}
.chapters .t{flex:1;font-size:.92rem}
.tag{color:var(--ok);font-weight:700}

/* study */
.banner{display:flex;align-items:center;gap:16px;padding:20px;border-radius:18px;margin-bottom:16px;color:#fff;background:linear-gradient(120deg,color-mix(in srgb,var(--sc) 85%,#0b1222),color-mix(in srgb,var(--sc) 55%,#0b1222))}
.banner .ico{width:56px;height:56px;border-radius:16px;background:rgba(255,255,255,.18);color:#fff;flex:none}
.banner .ico svg{width:30px;height:30px}
.banner small{opacity:.85;letter-spacing:.04em}
.banner h2{margin:2px 0 0;font-size:1.5rem;line-height:1.2}
h3{margin:22px 0 8px;font-size:1.05rem}
.lead{color:var(--muted);font-size:1.02rem}
.concepts{display:grid;grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:10px}
.concept{padding:14px;border-radius:14px;background:color-mix(in srgb,var(--sc,var(--brand)) 9%,var(--card));border:1px solid color-mix(in srgb,var(--sc,var(--brand)) 22%,var(--line))}
.concept b{display:block;margin-bottom:4px;color:var(--sc,var(--brand));font-size:.8rem;text-transform:uppercase;letter-spacing:.06em}
.revise{list-style:none;padding:0;margin:0;display:grid;gap:8px}
.revise li{display:flex;gap:10px}
.revise li::before{content:"";flex:none;width:8px;height:8px;margin-top:.55em;border-radius:50%;background:var(--gold)}
.row{display:flex;flex-wrap:wrap;align-items:center;gap:8px;margin:14px 0}
.best{background:var(--brand-soft);color:var(--brand);padding:6px 12px;border-radius:99px;font-weight:600;font-size:.85rem}
textarea{width:100%;min-height:80px;padding:10px;border-radius:12px;border:1px solid var(--line);background:var(--bg);color:var(--text);font:inherit}

/* quiz */
.opts{display:grid;gap:8px;margin:14px 0}
.opt{display:flex;align-items:center;gap:12px;text-align:left;padding:12px 14px;border-radius:14px}
.opt i{flex:none;display:grid;place-items:center;width:28px;height:28px;border-radius:8px;background:var(--bg);font-style:normal;font-weight:600;font-size:.85rem}
.opt.right{background:var(--ok-bg);border-color:var(--ok)}
.opt.wrong{background:var(--bad-bg);border-color:var(--bad)}
.bar{height:8px;background:var(--line);border-radius:99px;overflow:hidden}
.bar i{display:block;height:100%;background:linear-gradient(90deg,var(--brand),var(--gold));border-radius:99px}
.expl{padding:12px;border-radius:12px;background:var(--brand-soft);margin-top:8px}
.meta{display:flex;justify-content:space-between;color:var(--muted);font-size:.9rem;margin-bottom:8px}
.score{font-family:"Bricolage Grotesque",sans-serif;font-size:3rem;font-weight:800;color:var(--brand);line-height:1.1}
.wrong-item{padding:12px;border-radius:12px;background:var(--bad-bg);margin:8px 0}

.table-wrap{overflow-x:auto}
table{width:100%;border-collapse:collapse}
th,td{padding:9px 8px;border-bottom:1px solid var(--line);text-align:left}
footer{text-align:center;color:var(--muted);font-size:.8rem;padding:20px 16px}

/* sign in dialog */
dialog{width:min(380px,calc(100% - 32px));border:1px solid var(--line);border-radius:18px;padding:22px;background:var(--card);color:var(--text);box-shadow:var(--shadow)}
dialog::backdrop{background:rgba(8,14,30,.55)}
dialog h2{margin:0 0 12px}
dialog label{display:block;font-size:.85rem;color:var(--muted);margin:10px 0 4px}
dialog input{width:100%;padding:10px 12px;border-radius:10px;border:1px solid var(--line);background:var(--bg);color:var(--text);font:inherit}
.pin-mask{-webkit-text-security:disc;text-security:disc;letter-spacing:.2em}
.auth-msg{min-height:1.2em;margin:8px 0 0;color:var(--bad);font-size:.88rem}
.link{border:0;background:none;color:var(--brand);padding:4px 0;text-decoration:underline}
.note{color:var(--muted);font-size:.78rem;margin:10px 0 0}

@media(max-width:820px){
  .layout{grid-template-columns:1fr}
  .hero{flex-direction:column;align-items:flex-start;padding:22px 20px;margin:12px 16px 0}
  .hero-art{width:100%;max-width:340px;align-self:center}
}
@media(prefers-reduced-motion:reduce){*{transition:none!important}}

/* mascot */
.mascot-img{flex:none;width:min(380px,44%);aspect-ratio:1;border-radius:24px;background:var(--mascot) center/cover no-repeat;box-shadow:0 14px 40px rgba(0,0,0,.35);border:3px solid rgba(255,255,255,.25)}
.logo-face{flex:none;display:block;width:42px;height:42px;border-radius:50%;background:var(--mascot) 56% 30%/290% no-repeat;border:2px solid #ffc23a}
@media(max-width:820px){.mascot-img{width:min(320px,86%);align-self:center}}
/* concept pop-up */
button.concept{display:block;width:100%;text-align:left;font:inherit;cursor:pointer;color:var(--text);transition:transform .12s,box-shadow .12s}
button.concept:hover{transform:translateY(-2px);box-shadow:var(--shadow)}
.concept .more{display:block;margin-top:8px;font-size:.78rem;font-weight:600;color:var(--sc,var(--brand))}
dialog.wide{width:min(720px,calc(100% - 24px));max-height:88vh;overflow:auto}
.c-head{display:flex;justify-content:space-between;align-items:flex-start;gap:12px}
.c-head h2{margin:2px 0 8px;font-size:1.4rem}
.c-sub{margin:0;color:var(--muted);font-size:.8rem;text-transform:uppercase;letter-spacing:.06em}
.c-h{display:flex;align-items:center;gap:10px;margin:16px 0 6px;font-size:1rem}
.pill{background:var(--brand-soft);color:var(--brand);padding:2px 10px;border-radius:99px;font-size:.75rem;font-weight:600}
.book-text{white-space:pre-line;background:var(--bg);border:1px solid var(--line);border-radius:12px;padding:14px;line-height:1.7;font-size:.95rem}

/* tables in concept pop-up */
dialog.wide{width:min(860px,calc(100% - 24px))}
.tbl-wrap{overflow-x:auto;border:1px solid var(--line);border-radius:12px}
.ctbl{width:100%;border-collapse:collapse;font-size:.9rem;line-height:1.45}
.ctbl th{background:var(--brand-soft);color:var(--text);text-align:left;padding:9px 10px;font-weight:700;white-space:nowrap}
.ctbl td{padding:8px 10px;border-top:1px solid var(--line);vertical-align:top;min-width:110px}
.ctbl tbody tr:nth-child(even) td{background:color-mix(in srgb,var(--bg) 70%,var(--card))}
.ctbl td:first-child{font-weight:600}

/* chapter map */
.omap,.omap-sub{list-style:none;margin:0;padding:0}
.omap{display:grid;gap:10px}
.omap>li{padding:12px 14px;border:1px solid var(--line);border-radius:14px;background:color-mix(in srgb,var(--sc,var(--brand)) 5%,var(--card))}
.omap>li>b{color:var(--sc,var(--brand))}
.omap b{font-weight:700}
.omap span{color:var(--text)}
.omap-sub{margin-top:8px;padding-left:12px;border-left:2px solid color-mix(in srgb,var(--sc,var(--brand)) 35%,var(--line));display:grid;gap:6px}
.omap-sub li{font-size:.92rem;line-height:1.5}
.omap-sub li b{font-weight:600}

/* subject photo banners */
.banner{min-height:190px;background-image:linear-gradient(100deg,rgba(6,12,28,.88) 0%,rgba(6,12,28,.62) 42%,rgba(6,12,28,.06) 100%),var(--bimg,none),linear-gradient(120deg,color-mix(in srgb,var(--sc) 85%,#0b1222),color-mix(in srgb,var(--sc) 55%,#0b1222));background-size:cover;background-position:center;box-shadow:var(--shadow)}
.banner h2,.banner small{text-shadow:0 2px 12px rgba(0,0,0,.55)}
.banner>div{max-width:min(640px,100%)}
/* Ask StudyBuddy: free offline helper */
.sbq-fab{position:fixed;right:18px;bottom:18px;z-index:60;display:inline-flex;align-items:center;gap:8px;padding:12px 18px;border:0;border-radius:999px;font:inherit;font-weight:700;color:var(--on-brand);background:linear-gradient(135deg,var(--hero-b),var(--brand));box-shadow:var(--shadow);cursor:pointer}
.sbq-fab:hover{filter:brightness(1.07)}
.sbq-fab-ico{display:grid;place-items:center;width:22px;height:22px;border-radius:50%;background:rgba(255,255,255,.28);font-weight:800}
.sbq-panel{position:fixed;right:18px;bottom:84px;z-index:61;display:flex;flex-direction:column;width:min(400px,calc(100vw - 32px));height:min(600px,calc(100vh - 110px));background:var(--card);color:var(--text);border:1px solid var(--line);border-radius:18px;box-shadow:0 18px 50px rgba(0,0,0,.3);overflow:hidden}
.sbq-panel[hidden]{display:none}
.sbq-head{display:flex;justify-content:space-between;gap:10px;align-items:center;padding:12px 14px;color:#fff;background:linear-gradient(120deg,var(--hero-a),var(--hero-b))}
.sbq-title strong{display:block;font-family:"Bricolage Grotesque",Figtree,sans-serif}
.sbq-title span{font-size:.78rem;opacity:.85}
.sbq-close{border:0;background:transparent;color:#fff;font-size:1rem;padding:6px 8px;border-radius:8px}
.sbq-log{flex:1;overflow-y:auto;padding:12px;display:flex;flex-direction:column;gap:10px;font-size:.92rem}
.sbq-msg{padding:10px 12px;border-radius:14px;line-height:1.5;max-width:100%}
.sbq-user{align-self:flex-end;background:var(--brand);color:var(--on-brand);border-bottom-right-radius:4px;max-width:88%;white-space:pre-wrap}
.sbq-bot{background:var(--bg);border:1px solid var(--line);border-bottom-left-radius:4px}
.sbq-bot p{margin:0 0 8px}.sbq-bot p:last-child{margin-bottom:0}
.sbq-list{margin:0 0 8px;padding-left:18px}.sbq-list li{margin-bottom:4px}
.sbq-src{font-size:.78rem;color:var(--muted)}
.sbq-acts,.sbq-chips{display:flex;flex-wrap:wrap;gap:6px;margin-top:8px}
.sbq-act,.sbq-chip{padding:6px 10px;border-radius:999px;font-size:.8rem;border:1px solid var(--line);background:var(--card);color:var(--text);cursor:pointer}
.sbq-act{color:var(--brand);font-weight:600}
.sbq-form{display:flex;gap:8px;padding:10px 12px 0;border-top:1px solid var(--line)}
.sbq-form textarea{flex:1;resize:none;padding:9px 11px;border:1px solid var(--line);border-radius:12px;background:var(--bg);color:var(--text);font:inherit}
.sbq-send{align-self:flex-end;padding:9px 14px;border:0;border-radius:12px;background:var(--brand);color:var(--on-brand);font-weight:700;cursor:pointer}
.sbq-foot{margin:6px 12px 10px;font-size:.72rem;color:var(--muted)}
.sbq-tbl{margin:6px 0}
@media(max-width:640px){.sbq-fab-txt{display:none}.sbq-fab{padding:12px}.sbq-panel{inset:0;width:100%;height:100%;border-radius:0;border:0}}

/* downloads tab: one-pager list */
.dl-group{margin-top:16px}
.dl-group h3{display:flex;align-items:center;gap:10px;margin:0 0 10px}
.dl-group h3 .ico{width:32px;height:32px;color:var(--sc,var(--brand));background:color-mix(in srgb,var(--sc,var(--brand)) 16%,var(--card))}
.dl-group h3 .ico svg{width:18px;height:18px}
.dl-list{list-style:none;margin:0;padding:0;display:grid;gap:6px}
.dl-list li{display:flex;align-items:center;gap:10px;padding:9px 10px;border-radius:12px;background:color-mix(in srgb,var(--sc,var(--brand)) 5%,var(--card));border:1px solid var(--line)}
.dl-list .t{flex:1;font-size:.94rem}
.dl-btn{white-space:nowrap;font-size:.85rem;padding:7px 12px;color:var(--sc,var(--brand));border-color:color-mix(in srgb,var(--sc,var(--brand)) 40%,var(--line))}
.dl-btn:hover{background:color-mix(in srgb,var(--sc,var(--brand)) 12%,var(--card))}

/* one-pager: hidden on screen, shown only when printing */
#printArea{display:none}
@media print{
  body.printing>*:not(#printArea){display:none!important}
  body.printing #printArea{display:block!important}
  @page{size:A4;margin:0}
}
.op-page{font-family:Figtree,system-ui,sans-serif;color:#1c2333;background:#f7f3ea;background-image:radial-gradient(circle,#00000010 1px,transparent 1px);background-size:14px 14px;padding:14mm 13mm;box-sizing:border-box;min-height:100%}
.op-head2{display:flex;align-items:flex-start;justify-content:space-between;gap:16px;border-bottom:4px solid var(--sc,#0b7a72);padding-bottom:10px;margin-bottom:12px}
.op-eyebrow{margin:0;text-transform:uppercase;letter-spacing:.08em;font-weight:700;font-size:.7rem;color:var(--sc,#0b7a72)}
.op-head2 h1{margin:3px 0 4px;font-family:"Bricolage Grotesque",Figtree,sans-serif;font-size:1.55rem;color:#1c2333}
.op-sub{margin:0;font-size:.82rem;color:#5b6472}
.op-head-right{flex:none;display:flex;align-items:center;gap:8px}
.op-icon2{flex:none;display:grid;place-items:center;width:42px;height:42px;border-radius:11px;background:color-mix(in srgb,var(--sc,#0b7a72) 16%,#fff);color:var(--sc,#0b7a72)}
.op-icon2 svg{width:22px;height:22px}
.op-pages-badge{background:var(--sc,#0b7a72);color:#fff;font-weight:700;font-size:.66rem;line-height:1.3;text-align:center;padding:5px 10px;border-radius:9px;white-space:nowrap}
.op-callout{display:flex;gap:12px;align-items:flex-start;padding:10px 13px;border-radius:9px;margin:10px 0;font-size:.82rem;line-height:1.5;break-inside:avoid}
.op-callout .op-tag{flex:none;width:58px;font-weight:800;font-size:.62rem;letter-spacing:.04em;text-transform:uppercase;line-height:1.25}
.op-remember{background:#fbeed7;border-left:5px solid #e08a2c;color:#4a2f0a}
.op-remember .op-tag{color:#b4590a}
.op-keyfacts{background:color-mix(in srgb,var(--sc,#0b7a72) 12%,#fff);border-left:5px solid var(--sc,#0b7a72)}
.op-keyfacts .op-tag{color:var(--sc,#0b7a72)}
.op-section{margin:12px 0;break-inside:avoid}
.op-sec-head{display:flex;align-items:center;gap:9px;margin-bottom:5px}
.op-badge{flex:none;background:var(--sc,#0b7a72);color:#fff;font-weight:800;font-size:.72rem;padding:3px 9px;border-radius:7px}
.op-sec-head h2{margin:0;font-family:"Bricolage Grotesque",Figtree,sans-serif;font-size:.98rem;color:#1c2333}
.op-sec-desc{margin:0 0 7px;font-size:.8rem;color:#5b6472;line-height:1.45}
.op-cards{display:grid;grid-template-columns:1fr 1fr;gap:7px}
.op-card{background:#fff;border:1px solid #e7e2d5;border-left:4px solid var(--sc,#0b7a72);border-radius:8px;padding:8px 10px;break-inside:avoid}
.op-card b{display:block;font-size:.78rem;margin-bottom:2px;color:#1c2333}
.op-card span{display:block;font-size:.73rem;color:#5b6472;line-height:1.4}
.op-num{display:inline-block;margin-right:6px;color:var(--sc,#0b7a72);font-weight:800}
.op-tbl-wrap{margin:10px 0;break-inside:avoid}
.op-tbl-title{margin:0 0 5px;font-weight:700;font-size:.82rem;color:var(--sc,#0b7a72)}
table.op-table{width:100%;border-collapse:collapse;font-size:.72rem}
table.op-table th{background:#1c2333;color:#fff;text-align:left;padding:5px 7px;font-weight:600}
table.op-table td{padding:5px 7px;border-bottom:1px solid #e7e2d5}
table.op-table tr:nth-child(even) td{background:#f0ece0}
.op-foot2{display:flex;justify-content:space-between;gap:10px;margin-top:12px;padding-top:7px;border-top:1px solid #e7e2d5;font-size:.66rem;color:#5b6472}