:root{
  --bg:#f5f4fb; --bg2:#ecebf7; --card:#ffffff; --ink:#1d1b2f; --ink2:#5b5874; --line:#e3e1f0;
  --brand:#7c5cff; --brand2:#00c2a8; --ok:#00b37e; --okbg:#e3f8ef; --bad:#e5484d; --badbg:#fdecec;
  --warn:#f5a524; --shadow:0 6px 24px rgba(40,30,90,.08); --r:18px;
  --grad:linear-gradient(135deg,#7c5cff 0%,#b05cff 45%,#ff6fa5 100%);
}
:root[data-theme="dark"]{
  --bg:#0f0e17; --bg2:#17162a; --card:#1b1a2e; --ink:#eeeefa; --ink2:#a7a5c4; --line:#2c2a45;
  --okbg:#0f3326; --badbg:#3a1518; --shadow:0 6px 24px rgba(0,0,0,.35);
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    --bg:#0f0e17; --bg2:#17162a; --card:#1b1a2e; --ink:#eeeefa; --ink2:#a7a5c4; --line:#2c2a45;
    --okbg:#0f3326; --badbg:#3a1518; --shadow:0 6px 24px rgba(0,0,0,.35);
  }
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--ink);font-family:'IBM Plex Sans Thai','Inter',system-ui,sans-serif;font-size:16px;line-height:1.65;padding-bottom:84px}
a{color:var(--brand);text-decoration:none}
b{font-weight:600}
.wrap{max-width:980px;margin:0 auto;padding:16px}

/* header */
.top{position:sticky;top:0;z-index:20;display:flex;align-items:center;gap:12px;padding:10px 16px;padding-top:max(10px,env(safe-area-inset-top));
  background:color-mix(in srgb,var(--bg) 82%,transparent);backdrop-filter:blur(14px);-webkit-backdrop-filter:blur(14px);border-bottom:1px solid var(--line)}
.brand{display:flex;align-items:center;gap:8px;color:var(--ink);font-family:Inter,sans-serif;font-size:18px;font-weight:700}
.brand small{font-size:11px;font-weight:700;color:#fff;background:var(--grad);padding:2px 8px;border-radius:99px;letter-spacing:.5px}
.logo{display:grid;place-items:center;width:32px;height:32px;border-radius:10px;background:var(--grad);color:#fff;font-size:20px;font-weight:800}
.topnav{display:none;margin-left:auto;gap:4px}
.topnav a{color:var(--ink2);padding:6px 12px;border-radius:10px;font-weight:500}
.topnav a.on{background:var(--card);color:var(--brand);box-shadow:var(--shadow)}
.theme{margin-left:auto;border:1px solid var(--line);background:var(--card);color:var(--ink);width:36px;height:36px;border-radius:10px;font-size:18px;cursor:pointer}
@media (min-width:820px){.topnav{display:flex}.theme{margin-left:8px}.bottomnav{display:none!important}body{padding-bottom:24px}}

.bottomnav{position:fixed;left:0;right:0;bottom:0;z-index:20;display:flex;justify-content:space-around;padding:6px 4px;padding-bottom:max(6px,env(safe-area-inset-bottom));
  background:color-mix(in srgb,var(--card) 92%,transparent);backdrop-filter:blur(14px);-webkit-backdrop-filter:blur(14px);border-top:1px solid var(--line)}
.bottomnav a{flex:1;display:flex;flex-direction:column;align-items:center;color:var(--ink2);font-size:11px;padding:4px 0;border-radius:12px}
.bottomnav i{font-style:normal;font-size:20px;line-height:1.2}
.bottomnav a.on{color:var(--brand)}
.bottomnav a.on i{transform:translateY(-1px)}

/* generic */
h1,h2,h3{line-height:1.3;margin:0 0 8px}
h1{font-size:26px}h2{font-size:21px}h3{font-size:17px}
.muted{color:var(--ink2)}
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--r);padding:18px;box-shadow:var(--shadow);margin-bottom:14px}
.grid{display:grid;gap:12px}
@media (min-width:640px){.g2{grid-template-columns:1fr 1fr}.g3{grid-template-columns:repeat(3,1fr)}}
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;border:0;border-radius:14px;padding:12px 18px;font:inherit;font-weight:600;cursor:pointer;background:var(--grad);color:#fff;box-shadow:0 6px 18px rgba(124,92,255,.3);transition:transform .12s}
.btn:active{transform:scale(.97)}
.btn.ghost{background:var(--card);color:var(--ink);border:1px solid var(--line);box-shadow:none}
.btn.ok{background:var(--ok);box-shadow:none}.btn.bad{background:var(--bad);box-shadow:none}
.btn.block{width:100%}
.btn:disabled{opacity:.45;cursor:not-allowed}
.row{display:flex;gap:10px;flex-wrap:wrap;align-items:center}
.chip{display:inline-flex;align-items:center;gap:6px;border:1px solid var(--line);background:var(--card);color:var(--ink);border-radius:99px;padding:7px 14px;font:inherit;font-size:14px;cursor:pointer;user-select:none}
.chip.on{background:var(--brand);border-color:var(--brand);color:#fff}
.tag{display:inline-block;font-size:12px;font-weight:600;padding:2px 10px;border-radius:99px;background:var(--bg2);color:var(--ink2)}
.katex{font-size:1.06em}
.katex-display{margin:.4em 0;overflow-x:auto;overflow-y:hidden;padding:4px 0}

/* hero */
.hero{position:relative;overflow:hidden;border-radius:24px;padding:22px;color:#fff;background:var(--grad);box-shadow:0 14px 40px rgba(124,92,255,.35);margin-bottom:16px}
.hero:after{content:'∫';position:absolute;right:-10px;bottom:-60px;font-size:220px;opacity:.13;font-weight:800}
.hero h1{font-size:24px}
.hero .sub{opacity:.92;font-size:14px}
.count{display:flex;gap:10px;margin:14px 0 4px}
.count div{background:rgba(255,255,255,.18);border-radius:14px;padding:8px 12px;min-width:62px;text-align:center}
.count b{display:block;font-family:Inter;font-size:24px;font-weight:800;line-height:1.1}
.count span{font-size:11px;opacity:.9}
.quick{display:grid;grid-template-columns:1fr 1fr;gap:10px;margin-bottom:16px}
@media (min-width:640px){.quick{grid-template-columns:repeat(4,1fr)}}
.qa{display:flex;flex-direction:column;gap:2px;background:var(--card);border:1px solid var(--line);border-radius:16px;padding:14px;color:var(--ink);box-shadow:var(--shadow)}
.qa i{font-style:normal;font-size:22px}
.qa b{font-size:15px}.qa span{font-size:12px;color:var(--ink2)}

/* chapter tiles */
.tiles{display:grid;gap:10px}
@media (min-width:640px){.tiles{grid-template-columns:1fr 1fr}}
.tile{display:flex;gap:14px;align-items:center;background:var(--card);border:1px solid var(--line);border-radius:16px;padding:14px;color:var(--ink);box-shadow:var(--shadow)}
.tile .ic{flex:0 0 46px;height:46px;border-radius:14px;display:grid;place-items:center;font-size:22px;font-weight:700;color:#fff}
.tile .t{flex:1;min-width:0}
.tile .t b{display:block;font-size:15px}
.tile .t span{font-size:12px;color:var(--ink2)}
.bar{height:6px;border-radius:9px;background:var(--bg2);overflow:hidden;margin-top:6px}
.bar i{display:block;height:100%;background:var(--grad);border-radius:9px}

/* lesson */
.lhead{border-radius:22px;padding:20px;color:#fff;margin-bottom:14px}
.lhead .n{font-family:Inter;font-weight:800;opacity:.85;font-size:13px;letter-spacing:1px}
.lhead h1{margin:2px 0 4px}
.sec{margin-bottom:14px}
.sec>h3{display:flex;align-items:center;gap:8px}
.sec>h3 .dot{width:26px;height:26px;border-radius:8px;display:grid;place-items:center;font-size:14px;color:#fff;background:var(--brand)}
ol.steps{margin:0;padding-left:0;list-style:none;counter-reset:s}
ol.steps li{counter-increment:s;position:relative;padding:8px 0 8px 38px;border-bottom:1px dashed var(--line)}
ol.steps li:last-child{border-bottom:0}
ol.steps li:before{content:counter(s);position:absolute;left:0;top:9px;width:26px;height:26px;border-radius:50%;background:var(--bg2);color:var(--brand);font-weight:700;font-size:13px;display:grid;place-items:center}
.flist{display:grid;gap:8px}
@media (min-width:640px){.flist{grid-template-columns:1fr 1fr}}
.f{background:var(--bg2);border-radius:14px;padding:10px 12px;overflow-x:auto}
.f small{display:block;color:var(--ink2);font-size:12px}
.tbl{width:100%;border-collapse:collapse;font-size:14px}
.tbl th,.tbl td{border-bottom:1px solid var(--line);padding:8px 6px;text-align:left;vertical-align:middle}
.tbl th{color:var(--ink2);font-weight:600;font-size:12px}
.scroll{overflow-x:auto}
.ex{border:1px solid var(--line);border-radius:16px;padding:14px;margin-bottom:10px;background:var(--card)}
.ex .q{font-weight:600;overflow-x:auto}
.ex .st{margin-top:8px}
.ex .st li{animation:pop .25s ease}
@keyframes pop{from{opacity:0;transform:translateY(4px)}to{opacity:1;transform:none}}
.trap{border-left:4px solid var(--bad);background:var(--badbg);border-radius:12px;padding:10px 12px;margin-bottom:8px;font-size:15px}
.tip{border-left:4px solid var(--warn);background:color-mix(in srgb,var(--warn) 14%,var(--card));border-radius:12px;padding:10px 12px;font-size:15px}
.note{border-left:4px solid var(--brand);background:color-mix(in srgb,var(--brand) 10%,var(--card));border-radius:12px;padding:12px 14px;font-size:14px}

/* quiz */
.qtop{display:flex;justify-content:space-between;align-items:center;margin-bottom:8px;font-size:14px;color:var(--ink2)}
.prog{height:8px;border-radius:9px;background:var(--bg2);overflow:hidden;margin-bottom:14px}
.prog i{display:block;height:100%;background:var(--grad);transition:width .3s}
.qcard{font-size:17px}
.qcard .qq{font-size:18px;margin:6px 0 14px;overflow-x:auto}
.opts{display:grid;gap:10px}
.opt{display:flex;gap:12px;align-items:center;text-align:left;width:100%;border:2px solid var(--line);background:var(--card);color:var(--ink);border-radius:14px;padding:12px 14px;font:inherit;cursor:pointer;transition:border-color .15s,background .15s;overflow-x:auto}
.opt .k{flex:0 0 30px;height:30px;border-radius:9px;background:var(--bg2);display:grid;place-items:center;font-weight:700;font-family:Inter;color:var(--ink2)}
.opt:hover{border-color:var(--brand)}
.opt.ok{border-color:var(--ok);background:var(--okbg)}.opt.ok .k{background:var(--ok);color:#fff}
.opt.bad{border-color:var(--bad);background:var(--badbg)}.opt.bad .k{background:var(--bad);color:#fff}
.opt:disabled{cursor:default}
.verdict{display:flex;align-items:center;gap:10px;font-weight:700;font-size:18px;margin:14px 0 6px}
.verdict.ok{color:var(--ok)}.verdict.bad{color:var(--bad)}
.sol{background:var(--bg2);border-radius:14px;padding:12px 14px;margin-top:8px}
.score{text-align:center;padding:26px 18px}
.score .big{font-family:Inter;font-size:56px;font-weight:800;background:var(--grad);-webkit-background-clip:text;background-clip:text;color:transparent;line-height:1.1}
.ring{width:120px;height:120px;margin:0 auto 8px}
.kv{display:flex;justify-content:space-between;padding:6px 0;border-bottom:1px dashed var(--line);font-size:14px}
.sticky-act{position:sticky;bottom:76px;z-index:5;padding-top:8px}
@media (min-width:820px){.sticky-act{bottom:12px}}

/* written */
.wq{border:1px solid var(--line);border-radius:16px;padding:14px;margin-bottom:12px;background:var(--card)}
.wq .hd{display:flex;justify-content:space-between;gap:8px;align-items:center;margin-bottom:6px}
.wq .p{font-size:17px;overflow-x:auto}
.ans{margin-top:10px;padding:10px 12px;border-radius:12px;background:var(--okbg);font-weight:600;overflow-x:auto}
.tabs{display:flex;gap:6px;overflow-x:auto;padding-bottom:4px;margin-bottom:12px}
.tabs::-webkit-scrollbar{display:none}
.sheet-grid{display:grid;gap:6px}
@media (min-width:640px){.sheet-grid{grid-template-columns:1fr 1fr}}
.sheet-grid .f{display:flex;gap:10px;align-items:center}
.sheet-grid .f .no{flex:0 0 26px;font-family:Inter;font-weight:700;color:var(--ink2);font-size:12px}
.foot{text-align:center;color:var(--ink2);font-size:12px;padding:20px 0 8px}
.empty{text-align:center;color:var(--ink2);padding:30px}

/* detailed-solution step labels */
.lbl{display:inline-block;font-size:12px;font-weight:700;padding:1px 9px;border-radius:99px;margin:0 4px 2px 0;vertical-align:1px;white-space:nowrap}
.lbl-b{background:color-mix(in srgb,#3b82f6 15%,var(--card));color:#3b82f6}
.lbl-p{background:color-mix(in srgb,#9b6bff 16%,var(--card));color:#8b5cf6}
.lbl-o{background:color-mix(in srgb,#f08c00 16%,var(--card));color:#d97706}
.lbl-r{background:color-mix(in srgb,#e5484d 15%,var(--card));color:#e5484d}
.lbl-g{background:color-mix(in srgb,#12a874 16%,var(--card));color:#12a874}
ol.steps li .katex-display{margin:.2em 0}
.legend{display:flex;flex-wrap:wrap;gap:6px 12px;font-size:12px;color:var(--ink2);margin:6px 0 2px}

/* beginner pages */
.tile.start{border:2px solid #00b894;margin-bottom:10px}
.bp{margin:8px 0}
.dgw{margin:8px 0 10px;padding:8px;border-radius:14px;background:var(--bg2)}
.dgw figcaption{font-size:12px;color:var(--ink2);text-align:center}
.dg{width:100%;height:auto;display:block;max-width:520px;margin:0 auto}
.dg .ax{stroke:var(--ink2);stroke-width:1.5;fill:none}
.dg .cv{stroke:#7c5cff;stroke-width:3;fill:none;stroke-linecap:round}
.dg .cv2{stroke:#00b894;stroke-width:3;fill:none;stroke-linecap:round}
.dg .dash{stroke-dasharray:6 5;opacity:.6}
.dg .hl{stroke:#f08c00;stroke-width:2.5;fill:none}
.dg .gd{stroke:#f08c00;stroke-width:1.5;stroke-dasharray:4 3}
.dg .pt{fill:#f08c00}
.dg .fl{fill:#7c5cff;opacity:.22;stroke:none}
.dg .fl2{fill:#00b894;opacity:.15}
.dg .hole{fill:var(--bg2)}
.dg .rc{fill:#7c5cff;opacity:.18;stroke:#7c5cff;stroke-width:.8}
.dg .tx{fill:var(--ink);font-size:12px;font-family:'IBM Plex Sans Thai',sans-serif}
.dg .tx.b{font-weight:700}
.chk{margin-top:10px;padding:12px;border-radius:14px;background:color-mix(in srgb,#00b894 10%,var(--card));border:1px dashed #00b894}
.chk details{margin-top:8px;padding:8px 10px;border-radius:10px;background:var(--card)}
.chk summary{cursor:pointer;font-weight:500}
.easy{border-left:5px solid #00b894}
.need{margin-top:10px;display:flex;flex-wrap:wrap;gap:6px;align-items:center;font-size:14px;color:var(--ink2)}
ol.flow{list-style:none;padding:0;margin:8px 0 0;counter-reset:f}
ol.flow li{counter-increment:f;position:relative;padding:10px 0 10px 40px;border-bottom:1px dashed var(--line)}
ol.flow li:before{content:counter(f);position:absolute;left:0;top:10px;width:28px;height:28px;border-radius:50%;background:#00b894;color:#fff;font-weight:700;display:grid;place-items:center;font-size:14px}
ol.flow li .chip{margin-top:6px;font-size:13px}
.kv.gl{align-items:flex-start;gap:12px;padding:10px 0}
.kv.gl a{white-space:nowrap;font-size:13px}
.tabs .chip{white-space:nowrap;flex:0 0 auto}

/* account button */
.acct{margin-left:auto;height:36px;border-radius:10px;border:1px solid var(--line);background:var(--card);color:var(--ink);padding:0 10px;display:inline-flex;align-items:center;gap:6px;font:inherit;font-size:13px;font-weight:600;cursor:pointer}
.acct+.theme{margin-left:8px}
.acct .g{font-family:Inter;font-weight:800;background:conic-gradient(from -45deg,#ea4335 0 25%,#fbbc05 0 50%,#34a853 0 75%,#4285f4 0);-webkit-background-clip:text;background-clip:text;color:transparent;font-size:16px}
.acct.in{padding:0;width:36px;overflow:hidden;justify-content:center}
.acct img{width:100%;height:100%;object-fit:cover}
@media (max-width:380px){.acct .t{display:none}}
@media (min-width:820px){.acct{margin-left:8px}}

/* login gate */
body.locked .bottomnav,body.locked .topnav,body.locked #acctBtn{display:none!important}
body.locked{padding-bottom:24px}
.gate{max-width:420px;margin:6vh auto 0;text-align:center;padding:0 4px}
.gate h1{margin:14px 0 6px}
.gate .btn{margin-top:14px}
.gate-logo{border-radius:22px;box-shadow:0 12px 32px rgba(124,92,255,.35)}
.gate-logo.pulse{animation:gp 1.2s ease-in-out infinite}
@keyframes gp{50%{transform:scale(.92);opacity:.7}}
.gbtn{background:#fff;color:#1f1f1f;border:1px solid #dadce0;box-shadow:0 2px 8px rgba(0,0,0,.08)}
.gbtn .g{font-family:Inter;font-weight:800;font-size:18px;background:conic-gradient(from -45deg,#ea4335 0 25%,#fbbc05 0 50%,#34a853 0 75%,#4285f4 0);-webkit-background-clip:text;background-clip:text;color:transparent}

.fbtn{background:#1877f2;color:#fff;box-shadow:0 4px 14px rgba(24,119,242,.3);margin-top:10px!important}
.fbtn .fi{flex:0 0 22px}