@font-face{font-family:Poppins;font-weight:700;font-display:swap;src:url(/assets/fonts/poppins-700.woff2) format("woff2")}
:root{--navy:#081c2c;--navy2:#0c2b40;--teal:#0d4f5f;--y:#ffd21f;--g:#39e27a;--gd:#0f8a43;--ink:#14212b;--mut:#56636e;--bg:#f4f7f9;--card:#fff;--line:#dfe6ec;--soft:#e9f2f5;--ok:#15803d;--okbg:#e7f7ec;--bad:#c62828;--badbg:#fdeaea;--link:#07677f;--hd:#081c2c;--sh:0 1px 2px rgba(8,28,44,.06),0 4px 14px rgba(8,28,44,.06)}
[data-theme=dark]{--ink:#e6eef3;--mut:#a3b3bf;--bg:#07131d;--card:#0e2131;--line:#1f3a4f;--soft:#12304a;--okbg:#0f3320;--badbg:#3a1414;--link:#7fd8ec;--hd:#fff;--ok:#4ade80;--bad:#f87171}
*{box-sizing:border-box}html{-webkit-text-size-adjust:100%;scroll-padding-top:76px}
body{margin:0;font:16.5px/1.68 system-ui,-apple-system,"Segoe UI",Roboto,"Noto Sans","Noto Sans Devanagari",sans-serif;color:var(--ink);background:var(--bg)}
body.big{font-size:18.5px}
h1,h2,h3,.btn,.brand b,.kick,.tabs button,.num{font-family:Poppins,system-ui,sans-serif}
h1{font-size:clamp(1.55rem,4.4vw,2.35rem);line-height:1.22;margin:.25em 0 .35em;color:var(--hd)}
h2{font-size:clamp(1.2rem,3.2vw,1.55rem);line-height:1.3;color:var(--hd);margin:1.7em 0 .6em}
h3{font-size:1.04rem;line-height:1.4;margin:0 0 .3em;color:var(--hd)}
a{color:var(--link)}img,svg{max-width:100%;height:auto}
.wrap{max-width:1120px;margin:0 auto;padding:0 18px}.narrow{max-width:780px}
.skip{position:absolute;left:-999px}.skip:focus{left:8px;top:8px;background:#fff;color:#000;padding:8px;z-index:99}
:focus-visible{outline:3px solid var(--y);outline-offset:2px}
.hi{font-family:"Noto Sans Devanagari",system-ui,sans-serif}
/* header */
.top{background:var(--navy);color:#fff;position:sticky;top:0;z-index:20;border-bottom:3px solid var(--y)}
.bar{display:flex;align-items:center;gap:12px;min-height:62px}
.brand{display:flex;align-items:center;gap:10px;color:#fff;text-decoration:none;margin-right:auto}
.brand img{border-radius:50%;width:40px;height:40px}.brand b{font-size:1.02rem;line-height:1.1}.brand small{display:block;font-size:.7rem;color:var(--g);font-weight:600;letter-spacing:.03em}
.nav{display:flex;gap:4px;align-items:center}.nav a{color:#dfe9f0;text-decoration:none;font-size:.92rem;padding:8px 10px;border-radius:8px}.nav a:hover,.nav a[aria-current]{color:var(--y);background:rgba(255,255,255,.06)}
.tools{display:flex;gap:6px}.tbtn{background:rgba(255,255,255,.08);color:#fff;border:1px solid rgba(255,255,255,.18);border-radius:8px;min-width:40px;height:38px;padding:0 9px;font:600 .85rem system-ui;cursor:pointer}
.tbtn:hover{border-color:var(--y)}
.mbtn{display:none}
@media(max-width:900px){.nav{display:none;position:absolute;top:65px;left:0;right:0;background:var(--navy2);flex-direction:column;align-items:stretch;padding:8px 12px 14px;border-bottom:3px solid var(--y)}.nav.open{display:flex}.nav a{padding:12px}.mbtn{display:inline-block}}
.bnav{display:none}
@media(max-width:700px){.bnav{display:flex;position:fixed;bottom:0;left:0;right:0;z-index:20;background:var(--navy);border-top:2px solid var(--y);justify-content:space-around;padding:4px 0 calc(4px + env(safe-area-inset-bottom))}.bnav a{color:#dbe6ee;text-decoration:none;font-size:.7rem;display:flex;flex-direction:column;align-items:center;gap:1px;padding:4px 6px;min-width:58px}.bnav a span{font-size:1.15rem;line-height:1.2}.bnav a[aria-current]{color:var(--y)}body{padding-bottom:64px}}
/* common */
.crumbs{font-size:.84rem;color:var(--mut);padding:14px 0 0}.crumbs a{color:var(--mut)}.crumbs ol{list-style:none;padding:0;margin:0;display:flex;flex-wrap:wrap;gap:4px}.crumbs li+li:before{content:"›";margin:0 5px 0 2px;opacity:.6}
.kick{color:var(--teal);font-weight:600;font-size:.8rem;letter-spacing:.04em;text-transform:uppercase;margin:8px 0 0}[data-theme=dark] .kick{color:var(--g)}
.h1hi{display:block;font-family:"Noto Sans Devanagari",system-ui,sans-serif;font-weight:600;font-size:.6em;line-height:1.6;color:var(--teal);margin-top:4px}[data-theme=dark] .h1hi{color:var(--y)}
.lead{font-size:1.06rem;color:var(--ink);opacity:.92}.mut{color:var(--mut)}.small{font-size:.88rem}
.btn{display:inline-flex;align-items:center;gap:6px;background:var(--y);color:#081c2c;font-weight:600;text-decoration:none;padding:11px 18px;border-radius:12px;margin:4px 6px 4px 0;border:2px solid var(--y);cursor:pointer;font-size:.95rem;line-height:1.2}
.btn:hover{filter:brightness(.96)}.btn.ghost{background:transparent;color:var(--hd);border-color:var(--line)}.btn.dark{background:var(--navy);border-color:var(--navy);color:#fff}.btn.sm{padding:7px 12px;font-size:.85rem;border-radius:10px}
.btn[disabled]{opacity:.5;cursor:not-allowed}
.chip{display:inline-block;background:var(--soft);color:var(--teal);font-size:.76rem;font-weight:600;padding:3px 10px;border-radius:20px;margin:0 4px 4px 0}[data-theme=dark] .chip{color:var(--g)}
.chip.y{background:#fff4c2;color:#5c4800}.chip.g{background:var(--okbg);color:var(--ok)}.chip.r{background:var(--badbg);color:var(--bad)}.chip.n{background:transparent;border:1px solid var(--line);color:var(--mut)}
.card{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:18px;box-shadow:var(--sh)}
.grid{display:grid;gap:14px}.g2{grid-template-columns:repeat(auto-fill,minmax(260px,1fr))}.g3{grid-template-columns:repeat(auto-fill,minmax(220px,1fr))}.g4{grid-template-columns:repeat(4,1fr)}
@media(max-width:760px){.g4{grid-template-columns:repeat(2,1fr)}}
a.card{text-decoration:none;color:var(--ink);display:block;transition:transform .12s,border-color .12s}a.card:hover{border-color:var(--teal);transform:translateY(-1px)}
.card .num{display:inline-grid;place-items:center;width:46px;height:46px;border-radius:12px;background:var(--navy);color:var(--y);font-weight:700;font-size:1.15rem}
.card b{display:block;font-size:1.05rem;margin-top:8px;color:var(--hd)}.card em{font-style:normal;color:var(--mut);font-size:.86rem;display:block}
.sec{padding:8px 0 10px}
.note{background:var(--soft);border-left:4px solid var(--teal);padding:12px 14px;border-radius:10px;font-size:.93rem;margin:14px 0}.note.y{border-color:var(--y);background:#fff8d6;color:#3d3200}[data-theme=dark] .note.y{background:#2b2606;color:#f6e7a6}
/* hero */
.hero{background:radial-gradient(1200px 400px at 85% -10%,rgba(57,226,122,.18),transparent),linear-gradient(135deg,#081c2c 0%,#0c3446 60%,#0d4f5f 100%);color:#fff;padding:34px 0 40px}
.hero h1{color:#fff;font-size:clamp(1.75rem,5.2vw,2.85rem)}.hero h1 em{font-style:normal;color:var(--y)}.hero .lead{color:#d5e3ec;max-width:640px}.hero .kick{color:var(--g)}
.hero .btn.ghost{color:#fff;border-color:rgba(255,255,255,.4)}
.hgrid{display:grid;grid-template-columns:1.4fr 1fr;gap:26px;align-items:center}@media(max-width:820px){.hgrid{grid-template-columns:1fr}}
.picker{background:rgba(255,255,255,.06);border:1px solid rgba(255,255,255,.16);border-radius:18px;padding:16px}
.picker h2{color:#fff;font-size:1.05rem;margin:0 0 10px}
.seg{display:flex;gap:6px;background:rgba(0,0,0,.25);padding:4px;border-radius:12px;margin-bottom:12px}.seg button{flex:1;border:0;border-radius:9px;padding:10px;background:transparent;color:#cfe0ea;font:600 .9rem Poppins,system-ui;cursor:pointer}.seg button[aria-pressed=true]{background:var(--y);color:#081c2c}
.cls{display:grid;grid-template-columns:repeat(4,1fr);gap:8px}.cls a{display:block;text-align:center;background:#fff;color:#081c2c;border-radius:12px;padding:12px 4px;text-decoration:none;font:700 1.25rem Poppins,system-ui}.cls a small{display:block;font:500 .7rem system-ui;color:#56636e}
.cls a:hover{outline:3px solid var(--g)}
.stats{display:flex;flex-wrap:wrap;gap:18px;margin-top:16px;color:#cfe0ea;font-size:.88rem}.stats b{color:var(--y);font:700 1.15rem Poppins;display:block}
/* lists */
.chlist{list-style:none;padding:0;margin:0;display:grid;gap:8px}
.chlist li a,.chlist li>div{display:flex;gap:12px;align-items:center;background:var(--card);border:1px solid var(--line);border-radius:12px;padding:11px 14px;text-decoration:none;color:var(--ink)}
.chlist li a:hover{border-color:var(--teal)}
.chlist .n{flex:0 0 34px;height:34px;border-radius:9px;background:var(--soft);display:grid;place-items:center;font:700 .9rem Poppins;color:var(--teal)}
.chlist .t{flex:1;min-width:0}.chlist .t small{display:block;color:var(--mut);font-size:.83rem}
.chlist .soon{opacity:.75}
.prog{font-size:.75rem;font-weight:700;color:var(--ok)}
details.sub{background:var(--card);border:1px solid var(--line);border-radius:14px;margin:0 0 10px}details.sub>summary{cursor:pointer;padding:14px 16px;font-weight:600;list-style:none;display:flex;gap:10px;align-items:center}
details.sub>summary::-webkit-details-marker{display:none}details.sub>summary:after{content:"+";margin-left:auto;font-size:1.3rem;color:var(--mut)}details.sub[open]>summary:after{content:"–"}
details.sub .in{padding:0 16px 14px}
.sub ol{margin:6px 0 10px;padding-left:22px}.sub ol li{margin:2px 0}
/* chapter */
.chhead{display:flex;flex-wrap:wrap;gap:6px;margin:6px 0 8px}
.layout{display:grid;grid-template-columns:230px 1fr;gap:28px;align-items:start}
.toc{position:sticky;top:80px;font-size:.88rem;background:var(--card);border:1px solid var(--line);border-radius:14px;padding:12px}
.toc b{display:block;margin-bottom:6px}.toc a{display:block;color:var(--ink);text-decoration:none;padding:5px 8px;border-radius:7px}.toc a:hover{background:var(--soft)}
@media(max-width:900px){.layout{grid-template-columns:1fr}.toc{position:static}.toc nav{display:flex;flex-wrap:wrap;gap:4px}.toc a{background:var(--soft);font-size:.8rem;padding:4px 10px}}
.modes{display:grid;grid-template-columns:repeat(3,1fr);gap:8px;margin:10px 0}.modes button{border:2px solid var(--line);background:var(--card);color:var(--ink);border-radius:12px;padding:10px 8px;cursor:pointer;text-align:left;font:600 .9rem Poppins,system-ui}.modes button small{display:block;font:400 .76rem system-ui;color:var(--mut)}
.modes button[aria-pressed=true]{border-color:var(--teal);background:var(--soft)}
@media(max-width:560px){.modes{grid-template-columns:1fr}.modes button{display:flex;gap:8px;align-items:baseline}}
.mode[hidden]{display:none}
.pts{display:grid;gap:10px;margin:0;padding:0;list-style:none}.pts li{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:13px 15px}.pts li h3{color:var(--teal)}[data-theme=dark] .pts li h3{color:var(--y)}
.pts.zero li{border-left:4px solid var(--g)}.pts.adv li{border-left:4px solid var(--y)}
.yt{position:relative;aspect-ratio:16/9;background:#000;border-radius:14px;overflow:hidden}.yt a,.yt iframe{position:absolute;inset:0;width:100%;height:100%;border:0}.yt img{width:100%;height:100%;object-fit:cover}
.yt .play{position:absolute;left:50%;top:50%;width:68px;height:48px;margin:-24px 0 0 -34px;background:#e00;border-radius:14px}.yt .play:after{content:"";position:absolute;left:27px;top:14px;border-style:solid;border-width:10px 0 10px 17px;border-color:transparent transparent transparent #fff}
.ytcap{font-size:.86rem;color:var(--mut);margin:6px 0 14px}
.shorts{display:flex;gap:10px;overflow-x:auto;padding-bottom:6px}.shorts a{flex:0 0 120px;aspect-ratio:9/16;border-radius:12px;overflow:hidden;position:relative;background:#000}.shorts img{width:100%;height:100%;object-fit:cover}
/* diagram */
.dg{background:var(--card);border:1px solid var(--line);border-radius:16px;overflow:hidden;margin:0 0 16px}
.dgbar{display:flex;flex-wrap:wrap;gap:6px;align-items:center;padding:8px 10px;border-bottom:1px solid var(--line);background:var(--soft)}
.dgbar b{margin-right:auto;font-size:.92rem}
.dgbar button{border:1px solid var(--line);background:var(--card);color:var(--ink);border-radius:8px;min-width:36px;height:34px;cursor:pointer;font-weight:700}
.dgv{position:relative;overflow:hidden;touch-action:none;background:#fff;max-height:72vh;cursor:grab}.dgv svg{position:absolute;left:0;top:0;width:100%;height:100%;transform-origin:0 0}
.dg.full{position:fixed;inset:0;z-index:50;border-radius:0;display:flex;flex-direction:column}.dg.full .dgv{flex:1;height:auto;max-height:none;aspect-ratio:auto!important}
.dg.nolbl .lbl{display:none}.dg [data-hs]{cursor:pointer}.dg [data-hs].on{filter:drop-shadow(0 0 4px #ffb800)}
.dginfo{padding:10px 14px;font-size:.92rem;border-top:1px solid var(--line);min-height:46px}
.dg figcaption{padding:8px 14px 12px;font-size:.86rem;color:var(--mut)}
/* quiz */
.q{background:var(--card);border:1px solid var(--line);border-radius:14px;padding:14px 16px;margin:0 0 12px}
.q .qt{font-weight:600;margin:0 0 8px}.q .meta{margin-bottom:6px}
.opts{display:grid;gap:7px}.opt{display:block;width:100%;text-align:left;border:1.5px solid var(--line);background:var(--bg);color:var(--ink);border-radius:10px;padding:10px 12px;cursor:pointer;font:inherit;font-size:.95rem}
.opt:hover{border-color:var(--teal)}.opt.sel{border-color:var(--teal);background:var(--soft)}.opt.ok{border-color:var(--ok);background:var(--okbg)}.opt.bad{border-color:var(--bad);background:var(--badbg)}
.exp{margin-top:8px;font-size:.92rem;background:var(--soft);border-radius:10px;padding:9px 12px}
.score{font-weight:700;margin:10px 0}
details.faq{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:12px 15px;margin:0 0 8px}details.faq summary{cursor:pointer;font-weight:600}
table{border-collapse:collapse;width:100%;font-size:.9rem}th,td{border:1px solid var(--line);padding:7px 9px;text-align:left;vertical-align:top}th{background:var(--soft)}
.tw{overflow-x:auto}
/* test */
.tbar{position:sticky;top:65px;z-index:10;background:var(--card);border:1px solid var(--line);border-radius:14px;padding:10px 12px;display:flex;flex-wrap:wrap;align-items:center;gap:10px;margin:10px 0;box-shadow:var(--sh)}
.timer{font:700 1.2rem Poppins;color:var(--hd)}.timer.low{color:var(--bad)}
.pal{display:flex;flex-wrap:wrap;gap:5px;margin:10px 0}.pal button{width:36px;height:36px;border-radius:9px;border:1.5px solid var(--line);background:var(--card);color:var(--ink);cursor:pointer;font-weight:600;font-size:.82rem}
.pal button.a{background:var(--teal);color:#fff;border-color:var(--teal)}.pal button.r{background:#fff1b8;border-color:#e0b400;color:#000}.pal button.cur{outline:3px solid var(--y)}
.legend{font-size:.78rem;color:var(--mut);display:flex;gap:12px;flex-wrap:wrap}
.bars .row{display:grid;grid-template-columns:150px 1fr 54px;gap:8px;align-items:center;font-size:.85rem;margin:4px 0}.bars .tr{background:var(--soft);border-radius:6px;height:10px;overflow:hidden}.bars .fl{background:var(--gd);height:100%}
@media(max-width:520px){.bars .row{grid-template-columns:96px 1fr 44px}}
/* filters */
.filters{display:flex;flex-wrap:wrap;gap:8px;margin:10px 0 14px}.filters select,.filters input{font:inherit;font-size:.9rem;padding:9px 10px;border-radius:10px;border:1px solid var(--line);background:var(--card);color:var(--ink);min-height:42px}
.filters input{flex:1;min-width:180px}
.res{display:grid;gap:10px}.res .card{padding:14px}.res .card h3{margin-bottom:4px}
.yeargrid{display:grid;grid-template-columns:repeat(auto-fill,minmax(92px,1fr));gap:6px}.yeargrid div{border-radius:10px;padding:8px;font-size:.78rem;text-align:center;border:1px solid var(--line);background:var(--card)}.yeargrid b{display:block;font:700 1rem Poppins}
.yeargrid .av{background:var(--okbg);border-color:var(--ok)}.yeargrid .na{background:var(--soft)}.yeargrid .old{background:#fff8d6;border-color:#e0b400;color:#3d3200}
/* cta + footer */
.cta{background:linear-gradient(135deg,#081c2c,#0d4f5f);color:#fff;border-radius:18px;padding:22px;display:flex;flex-wrap:wrap;gap:14px;align-items:center;justify-content:space-between;margin:26px 0}
.cta h2{color:#fff;margin:0;font-size:1.2rem}.cta p{margin:4px 0 0;color:#cfe0ea}
.foot{background:var(--navy);color:#b9c9d4;margin-top:40px;padding:30px 0 20px;font-size:.88rem}.foot a{color:#e4edf2;text-decoration:none}.foot a:hover{color:var(--y)}
.fgrid{display:grid;grid-template-columns:2fr 1fr 1fr 1fr;gap:20px}@media(max-width:760px){.fgrid{grid-template-columns:1fr 1fr}}
.foot h3{color:#fff;font-size:.95rem}.foot ul{list-style:none;padding:0;margin:0}.foot li{margin:5px 0}
.copy{border-top:1px solid #1b3a50;margin-top:18px;padding-top:14px;font-size:.8rem}
@media print{.top,.bnav,.foot,.toc,.modes,.tools,.yt,.cta,.noprint,.quizwrap{display:none!important}body{background:#fff;color:#000;font-size:12pt}.mode[hidden]{display:block!important}.layout{display:block}.pts li{break-inside:avoid;border:1px solid #ccc}}
@media(prefers-reduced-motion:reduce){*{transition:none!important;scroll-behavior:auto!important}}
@media(max-width:480px){.brand small{display:none}.brand b{font-size:.95rem}#sizebtn{display:none}.bar{gap:8px}.tbtn{min-width:36px;padding:0 7px}}
#qbox{scroll-margin-top:140px}
.sub ol i{font-style:normal;color:var(--mut);font-size:.86em;font-family:'Noto Sans Devanagari',system-ui,sans-serif}
.hfoot{grid-column:1/-1}@media(max-width:820px){.hero{padding:22px 0 26px}.stats{gap:10px 18px}.stats span{flex:1 1 40%}}

.tbtn.lang{display:inline-flex;align-items:center;gap:0;padding:0 3px;font-size:.78rem}.tbtn.lang b,.tbtn.lang i{font-style:normal;font-weight:600;padding:3px 6px;border-radius:6px;opacity:.6}html:not([data-ui=hi]) .tbtn.lang b,html[data-ui=hi] .tbtn.lang i{background:var(--y);color:#081c2c;opacity:1}
html:not([data-ui=hi]) .h1hi.ui{display:none}
/* ---- V3: labels, exams, PYQ links, lab, dashboard, low-data, toast ---- */
.lb{display:inline-block;font:600 .72rem/1.2 system-ui;padding:3px 7px;border-radius:6px;margin:2px 4px 2px 0;vertical-align:middle;border:1px solid}
.lb-o{background:#e8f1ff;color:#1d4ed8;border-color:#bfd5ff}.lb-f{background:#eaf7ef;color:#166534;border-color:#bfe6cc}.lb-s{background:#fff6d6;color:#7a5a00;border-color:#f3dd8a}.lb-m{background:#fdeaea;color:#a61b1b;border-color:#f5c2c2}
[data-theme=dark] .lb{filter:brightness(.92)}
.units{padding-left:1.2em}.units li{margin:.45em 0}.units .chip{display:inline-block;margin:3px 4px 0 0;text-decoration:none}
.toc{display:flex;flex-wrap:wrap;gap:6px;margin:8px 0 4px}.toc a{font-size:.85rem;padding:5px 10px;border:1px solid var(--line);border-radius:20px;background:var(--card);text-decoration:none}
.pplist{list-style:none;padding:0;margin:10px 0}.pp{display:flex;gap:10px;align-items:center;justify-content:space-between;background:var(--card);border:1px solid var(--line);border-radius:10px;padding:10px 12px;margin:6px 0}.pp .btn{white-space:nowrap;flex:none}
@media(max-width:560px){.pp{flex-direction:column;align-items:flex-start}}
.sim{margin:16px 0}.simgrid{display:grid;grid-template-columns:minmax(220px,1fr) 2fr;gap:16px}@media(max-width:760px){.simgrid{grid-template-columns:1fr}}
.rg{display:block;margin:0 0 10px;font-size:.92rem}.rg span{display:block}.rg input[type=range]{width:100%;accent-color:var(--gd);height:28px}.rg select{width:100%;padding:7px;border-radius:8px;border:1px solid var(--line);background:var(--card);color:var(--ink)}
.rg output{font-weight:700}.btnrow{display:flex;flex-wrap:wrap;gap:6px}
canvas.live{width:100%;height:270px;display:block;background:var(--soft);border-radius:10px;touch-action:pan-y}canvas.graph{width:100%;height:150px;display:block;margin-top:8px;background:var(--soft);border-radius:10px}
.res{display:flex;flex-wrap:wrap;gap:8px;margin:10px 0}.res span{flex:1 1 120px;background:var(--soft);border-radius:10px;padding:8px 10px;font-size:.8rem;color:var(--mut)}.res b{display:block;font-size:1.15rem;color:var(--hd)}
.numrow{display:flex;gap:8px;align-items:center}.numrow input{width:140px;padding:9px;border-radius:8px;border:1px solid var(--line);font-size:1rem;background:var(--card);color:var(--ink)}
.exp.okx{background:var(--okbg)}.exp.badx{background:var(--badbg)}
.bm{float:right;font-size:.8rem;border:1px solid var(--line);background:var(--card);color:var(--ink);border-radius:16px;padding:3px 10px;cursor:pointer;margin-left:8px}.bm[aria-pressed=true]{background:#fff6d6;color:#7a5a00;border-color:#f3dd8a}
.linkbtn{background:none;border:0;padding:0;color:var(--link);text-decoration:underline;cursor:pointer;font:inherit;font-size:.85rem}
.foot .linkbtn{color:inherit;font-size:inherit}
.rec{border-left:5px solid var(--gd)}
#toast{position:fixed;left:50%;bottom:84px;transform:translateX(-50%) translateY(20px);background:var(--navy);color:#fff;padding:10px 16px;border-radius:10px;max-width:92vw;opacity:0;transition:.25s;z-index:50;font-size:.9rem;pointer-events:none}#toast.show{opacity:1;transform:translateX(-50%)}
.lowdata .yt img{display:none}.lowdata .yt a{display:flex;align-items:center;justify-content:center;min-height:120px;background:var(--soft)}.lowdata .yt a::after{content:"▶ Low-data mode: tap to load the video";font-weight:600;color:var(--ink);padding:12px;text-align:center}
.dg.quizon [data-hs]{cursor:crosshair}
@media(max-width:1180px){.nav{display:none;position:absolute;top:65px;left:0;right:0;background:var(--navy2);flex-direction:column;align-items:stretch;padding:8px 12px 14px;border-bottom:3px solid var(--y)}.nav.open{display:flex}.nav a{padding:12px}.mbtn{display:inline-block}}
.flinks{display:flex;flex-wrap:wrap;gap:4px 14px;font-size:.88rem}.flinks a{color:inherit}.m3sel{display:flex;flex-wrap:wrap;gap:6px;margin:6px 0 10px}.m3sel .chip{cursor:pointer;font-size:.9rem;padding:7px 12px}.m3sel .chip[aria-pressed=true]{background:var(--navy);color:#fff}
.t3{margin:.2em 0 .4em;font-size:1.1rem}.v3d{position:relative;height:min(68vh,520px);border-radius:14px;overflow:hidden;background:radial-gradient(circle at 50% 40%,#1b3a52,#081c2c);touch-action:none}
.v3d canvas{width:100%;height:100%;display:block}.l3lay{position:absolute;inset:0;pointer-events:none}.l3{position:absolute;left:0;top:0;pointer-events:auto;font:600 11px/1.2 system-ui;color:#fff;background:rgba(8,28,44,.72);border:1px solid rgba(255,255,255,.35);border-radius:6px;padding:2px 6px;white-space:nowrap;cursor:pointer;margin:-9px 0 0 6px}
.v3d.nolab .l3{display:none}.v3load{position:absolute;inset:0;display:flex;align-items:center;justify-content:center;color:#cfe0ea}.v3d.ready .v3load{display:none}
.v3bar{display:flex;flex-wrap:wrap;gap:6px;margin:8px 0}.v3bar button{border:1px solid var(--line);background:var(--card);color:var(--ink);border-radius:8px;padding:7px 10px;font:600 .85rem system-ui;cursor:pointer}.v3bar button[aria-pressed=true]{background:var(--y);color:#000;border-color:var(--y)}
.full3{position:fixed;inset:0;z-index:60;background:var(--bg);padding:8px;overflow:auto}.full3 .v3d{height:calc(100vh - 170px)}
.v3d.nogl{height:auto;padding:16px;color:#fff}
/* ==================== PREMIUM LOOK v1 (2026-11-01) — appended layer; delete from here to the end to roll back ==================== */
:root{--navy:#071a26;--navy2:#0a2433;--teal:#0d4f5f;--teal2:#127985;--aqua:#7fd6cb;--y:#f8c93f;--y2:#ffd966;--g:#7fd6cb;--gd:#12808a;
--ink:#13202a;--mut:#5a6873;--bg:#f3f6f8;--card:#fff;--line:#e2e8ed;--soft:#ecf3f5;--link:#0b6676;--hd:#0a1b27;
--r:16px;--ease:cubic-bezier(.2,.7,.2,1);
--sh:0 1px 2px rgba(7,26,38,.05),0 6px 18px -8px rgba(7,26,38,.14);
--sh2:0 2px 4px rgba(7,26,38,.06),0 16px 32px -14px rgba(7,26,38,.28)}
[data-theme=dark]{--bg:#06121b;--card:#0c1e2b;--line:#1b3346;--soft:#11283a;--ink:#e4edf2;--mut:#9fb1bd;--link:#86dbe6;--hd:#f4f8fa;
--sh:0 1px 2px rgba(0,0,0,.3),0 8px 22px -10px rgba(0,0,0,.6);--sh2:0 2px 6px rgba(0,0,0,.35),0 18px 36px -14px rgba(0,0,0,.7)}
body{-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;text-rendering:optimizeLegibility}
h1,h2,h3{letter-spacing:-.012em}h1{letter-spacing:-.02em}
h2{font-size:clamp(1.22rem,3.4vw,1.6rem)}
::selection{background:rgba(248,201,63,.45)}
:focus-visible{outline:2px solid var(--y);outline-offset:3px;border-radius:6px}
.ic{width:1.15em;height:1.15em;flex:none;display:inline-block;vertical-align:-.2em}
/* header */
.top{background:rgba(7,26,38,.94);-webkit-backdrop-filter:saturate(150%) blur(14px);backdrop-filter:saturate(150%) blur(14px);border-bottom:1px solid rgba(248,201,63,.28);box-shadow:0 8px 24px -16px rgba(0,0,0,.7)}
.bar{min-height:60px}
.brand img{box-shadow:0 0 0 2px rgba(248,201,63,.55),0 4px 12px rgba(0,0,0,.35)}
.brand b{letter-spacing:-.01em}
.brand small{color:var(--aqua);font-weight:600;letter-spacing:.09em;font-size:.64rem;opacity:.9}
.nav a{border-radius:10px;transition:color .2s,background .2s}
.nav a:hover,.nav a[aria-current]{color:var(--y2);background:rgba(255,255,255,.07)}
@media(max-width:1180px){.nav{top:100%;background:rgba(10,36,51,.98);border-bottom:1px solid rgba(248,201,63,.25);box-shadow:0 18px 30px -18px rgba(0,0,0,.8);padding:6px 12px 12px}.nav a{border-radius:12px}.nav a+a{border-top:1px solid rgba(255,255,255,.05)}}
.tbtn{display:inline-grid;place-items:center;background:rgba(255,255,255,.06);border:1px solid rgba(255,255,255,.14);border-radius:11px;transition:background .2s,border-color .2s}
.tbtn:hover{border-color:rgba(248,201,63,.6);background:rgba(255,255,255,.1)}
.tbtn .ic{width:19px;height:19px}
.top .slh-lseg{border:1px solid rgba(255,255,255,.16);background:rgba(255,255,255,.05);padding:2px;gap:2px}
.top .slh-lseg button{border-radius:999px;min-height:30px;color:#dfe9f0;transition:background .2s,color .2s}
.top .slh-lseg button+button{border-left:0}
.top .slh-lseg button.on{background:var(--y);color:#0a1b27;box-shadow:0 2px 8px -2px rgba(248,201,63,.6)}
/* bottom nav */
@media(max-width:700px){
.bnav{background:rgba(7,26,38,.95);-webkit-backdrop-filter:saturate(150%) blur(14px);backdrop-filter:saturate(150%) blur(14px);border-top:1px solid rgba(255,255,255,.08);box-shadow:0 -10px 24px -18px rgba(0,0,0,.6);padding:5px 4px calc(5px + env(safe-area-inset-bottom))}
.bnav a{color:#9fb4c2;font-size:.68rem;font-weight:500;letter-spacing:.01em;gap:2px;padding:3px 4px;border-radius:12px;transition:color .2s}
.bnav a span{display:grid;place-items:center;width:44px;height:28px;border-radius:999px;font-size:1rem;transition:background .25s var(--ease)}
.bnav a span .ic{width:21px;height:21px}
.bnav a b{font-weight:600}
.bnav a[aria-current]{color:var(--y2)}
.bnav a[aria-current] span{background:rgba(248,201,63,.15)}
.bnav a:active span{background:rgba(255,255,255,.1)}
body{padding-bottom:70px}}
/* buttons + chips */
.btn{background:linear-gradient(180deg,var(--y2),var(--y));border:1px solid rgba(160,120,0,.25);color:#0a1b27;border-radius:13px;padding:12px 20px;letter-spacing:.005em;box-shadow:inset 0 1px 0 rgba(255,255,255,.55),0 8px 18px -10px rgba(200,150,0,.75);transition:transform .15s var(--ease),box-shadow .2s,filter .2s}
.btn:hover{filter:brightness(1.03);box-shadow:inset 0 1px 0 rgba(255,255,255,.55),0 12px 22px -10px rgba(200,150,0,.8)}
.btn:active{transform:translateY(1px) scale(.99)}
.btn.ghost{background:var(--card);color:var(--hd);border:1px solid var(--line);box-shadow:var(--sh)}
.btn.dark{background:linear-gradient(180deg,#0e3446,var(--navy));border-color:var(--navy);color:#fff;box-shadow:0 8px 18px -10px rgba(7,26,38,.7)}
.btn.sm{padding:8px 13px;border-radius:11px}
.hero .btn.ghost,.cta .btn.ghost{background:rgba(255,255,255,.06);color:#fff;border-color:rgba(255,255,255,.28);box-shadow:none}
.chip{border-radius:999px;font-weight:600;letter-spacing:.005em}
[data-theme=dark] .chip{color:var(--aqua)}
/* cards + lists */
.card{border-radius:var(--r);border-color:var(--line);box-shadow:var(--sh);padding:18px 18px}
a.card{transition:transform .25s var(--ease),box-shadow .25s var(--ease),border-color .25s}
a.card:hover{transform:translateY(-2px);box-shadow:var(--sh2);border-color:rgba(13,79,95,.35)}
a.card:active{transform:scale(.985)}
.card .num{width:46px;height:46px;border-radius:14px;background:linear-gradient(145deg,#11606f,#0a2f3d);color:var(--y2);box-shadow:inset 0 1px 0 rgba(255,255,255,.14),0 6px 14px -8px rgba(7,26,38,.8);font-size:1.05rem}
.card .num .ic{width:23px;height:23px}
.card b{letter-spacing:-.005em}
.card b .ic{color:var(--teal2);margin-right:6px;width:1.1em;height:1.1em}
[data-theme=dark] .card b .ic{color:var(--aqua)}
.chlist li a,.chlist li>div{border-radius:14px;box-shadow:var(--sh);transition:transform .2s var(--ease),border-color .2s,box-shadow .2s}
.chlist li a:hover{border-color:rgba(13,79,95,.35);box-shadow:var(--sh2)}.chlist li a:active{transform:scale(.99)}
.chlist .n{border-radius:11px;background:linear-gradient(145deg,#e3f1f3,#d3e8ec);color:var(--teal)}
[data-theme=dark] .chlist .n{background:var(--soft);color:var(--aqua)}
details.sub,details.faq,.q,.pts li,.pp,.toc{border-radius:14px;box-shadow:var(--sh)}
.note{border-radius:12px;border-left-width:3px}
.opt{border-radius:12px;transition:border-color .15s,background .15s}
.kick{color:var(--teal2);letter-spacing:.08em;font-size:.74rem}
[data-theme=dark] .kick{color:var(--aqua)}
.lb-f{background:#e6f5f3;color:#0b5f63;border-color:#bfe3de}
.rec{border-left-color:var(--teal2)}
/* hero */
.hero{background:radial-gradient(900px 380px at 90% -12%,rgba(64,190,180,.22),transparent 70%),radial-gradient(700px 300px at -10% 110%,rgba(248,201,63,.08),transparent 70%),linear-gradient(160deg,#061722 0%,#0a2a39 55%,#0d4a59 100%);position:relative}
.hero:after{content:"";position:absolute;left:0;right:0;bottom:0;height:1px;background:linear-gradient(90deg,transparent,rgba(248,201,63,.35),transparent)}
.hero .kick{color:var(--aqua);opacity:.95}
.hero h1 em{color:var(--y2);background:linear-gradient(180deg,#ffe28a,#f5c02f);-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent}
.picker{background:linear-gradient(160deg,rgba(255,255,255,.09),rgba(255,255,255,.03));border-color:rgba(255,255,255,.13);border-radius:20px;box-shadow:0 20px 40px -24px rgba(0,0,0,.7)}
.seg{background:rgba(0,0,0,.28);border-radius:13px}.seg button{border-radius:10px;transition:background .2s,color .2s}
.seg button[aria-pressed=true]{background:linear-gradient(180deg,var(--y2),var(--y));box-shadow:0 4px 12px -6px rgba(248,201,63,.8)}
.cls a{border-radius:14px;box-shadow:0 6px 14px -8px rgba(0,0,0,.6);transition:transform .2s var(--ease),box-shadow .2s}
.cls a:hover{outline:2px solid var(--y);outline-offset:0}.cls a:active{transform:scale(.96)}
.stats b{color:var(--y2)}
/* cta + footer */
.cta{background:radial-gradient(500px 200px at 100% 0,rgba(64,190,180,.2),transparent 70%),linear-gradient(140deg,#071a26,#0d4a59);border-radius:20px;box-shadow:var(--sh2);padding:24px 22px}
.foot{background:linear-gradient(180deg,#071a26,#04111a);border-top:1px solid rgba(248,201,63,.22);color:#a9bccb;padding:34px 0 24px}
.foot h3{font-size:1.02rem;letter-spacing:-.005em}
.foot .soc{display:flex;flex-wrap:wrap;gap:8px;margin:12px 0 16px}
.foot .soc a{display:inline-flex;align-items:center;gap:8px;padding:8px 14px;border-radius:999px;background:rgba(255,255,255,.06);border:1px solid rgba(255,255,255,.12);color:#eef4f7;font-weight:600;font-size:.86rem;transition:background .2s,border-color .2s}
.foot .soc a:hover{background:rgba(255,255,255,.1);border-color:rgba(248,201,63,.5);color:#fff}
.foot .soc .ic{width:18px;height:18px}
.flinks{gap:6px 16px}.flinks a{color:#c9d7e1}.flinks a:hover{color:var(--y2)}
.copy{border-top-color:rgba(255,255,255,.07);color:#8ea3b2;line-height:1.55}
/* tests + toast + 3D bar */
.tbar{border-radius:16px}
.pal button{border-radius:10px}
.bars .fl{background:linear-gradient(90deg,var(--teal2),#3fb3a9)}
#toast{background:rgba(7,26,38,.96);border:1px solid rgba(255,255,255,.1);border-radius:12px;box-shadow:var(--sh2)}
.v3bar button{border-radius:10px}.v3bar button[aria-pressed=true]{background:var(--y);border-color:var(--y)}
.m3sel .chip[aria-pressed=true]{background:var(--teal);color:#fff}
.dg{border-radius:var(--r);box-shadow:var(--sh)}
.yt{border-radius:var(--r);box-shadow:var(--sh2)}
@media(max-width:480px){.wrap{padding:0 16px}.card{padding:16px}}
@media(prefers-reduced-motion:reduce){a.card:hover,.btn:active{transform:none}}
.card>h2:first-child,.card>h3:first-child{margin-top:.15em}.brand>span{line-height:1.2}
/* 390px overflow fixes (legacy chapter TOC, long PYQ source lines) */.layout>*{min-width:0}.toc nav{flex-wrap:wrap;min-width:0;max-width:100%}.res>.card,.res .card{min-width:0;max-width:100%}.card p,.card b{overflow-wrap:anywhere}