/* Science Platform: dark first, light follows the phone/OS (or the moon button) */
:root{--bg:#071a1f;--bg2:#0b2228;--card:#0e262d;--card2:#123038;--ink:#eaf3f2;--mute:#94b0b3;--line:#1d3d45;--green:#24c884;--green-ink:#03251a;--green2:#0e3a30;--red:#ff8b7b;--red2:#3a1d19;--blue:#8db0ff;--blue2:#18274a;--amber:#f2c66b;--amber2:#33290f;--shadow:0 6px 24px rgba(0,0,0,.28);color-scheme:dark}
@media(prefers-color-scheme:light){:root:not([data-theme="dark"]){--bg:#f1f6f5;--bg2:#e6efee;--card:#fff;--card2:#f6faf9;--ink:#003440;--mute:#4f6a70;--line:#d5e3e2;--green:#0f9963;--green-ink:#fff;--green2:#dcf3ea;--red:#b83a2c;--red2:#fbe7e3;--blue:#1f4fd1;--blue2:#e6edfc;--amber:#8a5a00;--amber2:#fdf0d0;--shadow:0 6px 20px rgba(20,40,30,.08);color-scheme:light}}
:root[data-theme="light"]{--bg:#f1f6f5;--bg2:#e6efee;--card:#fff;--card2:#f6faf9;--ink:#003440;--mute:#4f6a70;--line:#d5e3e2;--green:#0f9963;--green-ink:#fff;--green2:#dcf3ea;--red:#b83a2c;--red2:#fbe7e3;--blue:#1f4fd1;--blue2:#e6edfc;--amber:#8a5a00;--amber2:#fdf0d0;--shadow:0 6px 20px rgba(20,40,30,.08);color-scheme:light}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--ink);font-family:"Hind Siliguri","Nirmala UI","Noto Sans Bengali",system-ui,sans-serif;font-size:16px;line-height:1.65}
header{display:flex;align-items:center;justify-content:space-between;gap:10px;min-height:60px;padding:10px max(16px,env(safe-area-inset-right,0px)) 10px max(16px,env(safe-area-inset-left,0px));background:color-mix(in srgb,var(--bg) 88%,transparent);backdrop-filter:blur(10px);border-bottom:1px solid var(--line);position:sticky;top:0;z-index:20}
.brand{display:flex;align-items:center;gap:9px;font-family:"Anek Bangla","Hind Siliguri",sans-serif;font-weight:700;font-size:17px;white-space:nowrap}
.logo{display:inline-flex}.logo img{height:30px;width:auto;display:block}.logo.big img{height:58px}
.logo .lg-l{display:none}
@media(prefers-color-scheme:light){:root:not([data-theme="dark"]) .logo .lg-l{display:block}:root:not([data-theme="dark"]) .logo .lg-d{display:none}}
:root[data-theme="light"] .logo .lg-l{display:block}:root[data-theme="light"] .logo .lg-d{display:none}
:root[data-theme="dark"] .logo .lg-d{display:block}:root[data-theme="dark"] .logo .lg-l{display:none}
.brand .pill{font-family:"Hind Siliguri",sans-serif;font-weight:600}
header .r{display:flex;align-items:center;gap:8px;font-size:14px;min-width:0}
.iconbtn{width:38px;height:38px;padding:0;display:grid;place-items:center;border-radius:12px;background:var(--card);color:var(--ink);border:1px solid var(--line)}
a{color:var(--blue)}
main{max-width:780px;margin:0 auto;padding:16px max(16px,env(safe-area-inset-right,0px)) 40px max(16px,env(safe-area-inset-left,0px))}
.card{background:var(--card);border:1px solid var(--line);border-radius:18px;padding:16px;margin-bottom:12px;box-shadow:var(--shadow)}
h1,h2,h3{font-family:"Anek Bangla","Hind Siliguri",sans-serif;margin:0}
h2{margin:2px 0 10px;font-size:22px}
h3{margin:0 0 8px;font-size:17px}
.hero{margin:6px 0 14px}.hero h2{font-size:24px}.hero p{margin:2px 0 0;color:var(--mute)}
label{display:block;font-size:13px;color:var(--mute);margin:12px 0 5px}
label:first-child{margin-top:0}
input,select,textarea{width:100%;padding:12px 13px;border:1px solid var(--line);border-radius:12px;background:var(--bg2);color:var(--ink);font:inherit}
textarea{min-height:170px;font-family:ui-monospace,Menlo,monospace;font-size:13px}
:focus-visible{outline:2px solid var(--green);outline-offset:2px}
button{font:inherit;border:0;border-radius:12px;padding:11px 18px;cursor:pointer;background:var(--green);color:var(--green-ink);font-weight:600}
button.ghost{background:transparent;color:var(--ink);border:1px solid var(--line);font-weight:500}
button.danger{background:var(--red);color:var(--bg)}
button.small{padding:6px 12px;font-size:13px;border-radius:10px}
button.full{width:100%;padding:14px;font-size:17px}
button:disabled{opacity:.45;cursor:default}
.row{display:flex;gap:10px;flex-wrap:wrap}.row>*{flex:1;min-width:140px}
.mute{color:var(--mute);font-size:14px}
.err{color:var(--red);margin:8px 0;font-size:14px}.ok{color:var(--green)}
.seg{display:flex;flex-wrap:wrap;gap:6px}
.seg button{background:var(--card2);color:var(--ink);border:1px solid var(--line);font-weight:500;padding:8px 14px;font-size:15px;border-radius:99px}
.seg button.on{background:var(--green);color:var(--green-ink);border-color:var(--green);font-weight:600}
header .seg button{padding:5px 11px;font-size:13px}
.tabs{display:flex;gap:6px;margin:0 0 14px;overflow-x:auto;padding:5px;background:var(--card);border:1px solid var(--line);border-radius:18px;scrollbar-width:none}
.tabs::-webkit-scrollbar{display:none}
.tabs button{flex:1 0 auto;background:transparent;color:var(--mute);white-space:nowrap;border-radius:13px;font-weight:500;padding:10px 16px}
.tabs button.on{background:var(--green);color:var(--green-ink);font-weight:600}
.lbl{font-size:13px;color:var(--mute);margin:14px 0 8px}
.tiles{display:grid;grid-template-columns:repeat(auto-fill,minmax(98px,1fr));gap:8px}
.tile{display:flex;flex-direction:column;align-items:center;gap:6px;text-align:center;font-size:14px;line-height:1.35;padding:14px 6px 11px;border-radius:16px;background:var(--card2);color:var(--ink);border:1.5px solid var(--line);font-weight:600}
.tile svg{width:34px;height:34px;color:var(--green)}
.tile small{display:block;color:var(--mute);font-weight:400;font-size:12px;line-height:1.3}
.tile.on{border-color:var(--green);background:var(--green2)}
.sec{background:var(--card);border:1px solid var(--line);border-radius:18px;overflow:hidden;margin-bottom:12px}
.sec>.hd{display:flex;align-items:center;gap:10px;padding:13px 16px;background:var(--card2);border-bottom:1px solid var(--line);font-family:"Anek Bangla","Hind Siliguri",sans-serif;font-weight:700}
.sec>.hd:before{content:"";width:4px;height:20px;border-radius:3px;background:var(--green)}
.badge{margin-left:auto;min-width:28px;text-align:center;padding:1px 9px;border-radius:99px;background:var(--bg2);border:1px solid var(--line);font-size:13px;color:var(--green);font-weight:600}
.acc{border-top:1px solid var(--line)}.acc:first-of-type{border-top:0}
.acc>summary{list-style:none;display:flex;align-items:center;gap:12px;padding:14px 16px;cursor:pointer}
.acc>summary::-webkit-details-marker{display:none}
.acc>summary .t{flex:1;min-width:0}.acc>summary .t b{display:block}
.acc>summary .n{color:var(--mute);font-size:14px}
.acc>summary:after{content:"";width:9px;height:9px;border-right:2px solid var(--green);border-bottom:2px solid var(--green);transform:rotate(45deg);margin:0 4px 4px;transition:transform .15s}
.acc[open]>summary:after{transform:rotate(225deg);margin-bottom:-2px}
.acc .body{padding:0 16px 16px}
.acc.off>summary{opacity:.55}
.chips{display:flex;flex-wrap:wrap;gap:6px;margin:0 0 12px}
.chip{display:inline-flex;gap:6px;align-items:center;padding:3px 11px;border-radius:99px;background:var(--bg2);border:1px solid var(--line);font-size:13px;color:var(--mute)}
.chap{display:flex;justify-content:space-between;align-items:center;gap:12px;padding:12px 0;border-top:1px solid var(--line)}
.chap:first-child{border-top:0}.chap>div{min-width:0}
.timer{position:sticky;top:60px;z-index:5;background:var(--card);border:1px solid var(--line);border-radius:14px;padding:8px 14px;display:flex;justify-content:space-between;align-items:center;margin-bottom:8px;box-shadow:var(--shadow)}
.timer b{font-family:"Anek Bangla",sans-serif;font-size:21px;font-variant-numeric:tabular-nums}
.timer.low b{color:var(--red)}
.prog{height:5px;background:var(--line);border-radius:4px;overflow:hidden;margin:0 0 12px}.prog i{display:block;height:100%;background:var(--green);width:0;transition:width .2s}
.q{padding:18px 0;border-top:1px solid var(--line)}.q:first-child{border-top:0;padding-top:2px}
.qt{font-size:17px;margin-bottom:8px;overflow-wrap:anywhere}.qt>b{float:left;margin-right:6px}.qt .src{display:inline-block;margin:4px 0 0;font-size:12px;color:var(--mute);background:var(--bg2);border:1px solid var(--line);border-radius:99px;padding:0 9px;white-space:nowrap}
.qt b{font-family:"Anek Bangla",sans-serif;color:var(--green);margin-right:6px}
.fig{display:block;max-width:100%;max-height:320px;margin:10px auto;border-radius:12px;background:#fff;padding:4px}
.opt{display:flex;gap:8px;width:100%;text-align:left;margin:8px 0;padding:12px 14px;border:1.5px solid var(--line);border-radius:14px;background:var(--card2);color:var(--ink);font-weight:400;align-items:baseline;overflow-wrap:anywhere}
.opt .l{flex:none;min-width:24px;font-weight:700;color:var(--green)}
.opt .tx{flex:1;min-width:0}
.opt.sel{border-color:var(--blue);background:var(--blue2)}
.opt.ok{border-color:var(--green);background:var(--green2)}
.opt.bad{border-color:var(--red);background:var(--red2)}
.tag{flex:none;font-size:12px;font-weight:600;margin-left:auto;color:var(--mute)}
.expl{background:var(--bg2);border:1px solid var(--line);border-left:4px solid var(--green);border-radius:12px;padding:10px 14px;margin-top:10px;font-size:16px}
.expl .h{font-weight:700;color:var(--green);margin-bottom:2px}
.ln{margin:3px 0;overflow-wrap:anywhere}
.eq{margin:4px 0}
.score{font-family:"Anek Bangla",sans-serif;font-size:50px;font-weight:700;color:var(--green);line-height:1.1}
.center{text-align:center}
.scroll{overflow-x:auto}
/* equations: real KaTeX, a little larger, never clipped (long ones scroll) */
.katex{font-size:1.1em;text-indent:0}
.katex-display{margin:.35em 0;padding:3px 0;overflow-x:auto;overflow-y:hidden;max-width:100%}
.katex-display>.katex{max-width:100%}
.qt .katex,.opt .katex{font-size:1.08em}
table{width:100%;border-collapse:collapse;font-size:15px;font-variant-numeric:tabular-nums}
th{font-size:12px;color:var(--mute);letter-spacing:.3px}
th,td{text-align:left;padding:9px 6px;border-top:1px solid var(--line);vertical-align:top}
tr:first-child th{border-top:0}
.pill{display:inline-block;padding:1px 10px;border-radius:99px;font-size:12px;background:var(--green2);color:var(--green)}
.pill.off{background:var(--red2);color:var(--red)}.pill.blue{background:var(--blue2);color:var(--blue)}.pill.amber{background:var(--amber2);color:var(--amber)}
.note{background:var(--amber2);color:var(--amber);border-radius:12px;padding:9px 13px;font-size:14px;margin-top:12px}
.bar{display:inline-block;height:8px;border-radius:4px;background:var(--green);vertical-align:middle;margin-right:6px}.bar.low{background:var(--red)}
.kpis{display:grid;grid-template-columns:repeat(auto-fit,minmax(130px,1fr));gap:10px;margin-bottom:12px}
.kpi{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:12px 14px}
.kpi b{display:block;font-family:"Anek Bangla",sans-serif;font-size:28px;line-height:1.2;color:var(--green)}
.kpi span{font-size:13px;color:var(--mute)}
.spark{display:flex;align-items:flex-end;gap:4px;height:64px}
.spark i{flex:1;background:var(--green);border-radius:4px 4px 0 0;min-height:3px;opacity:.9}
.spark.lo i{background:var(--blue)}
.avatar{width:64px;height:64px;border-radius:20px;background:var(--green2);color:var(--green);display:grid;place-items:center;font-family:"Anek Bangla",sans-serif;font-size:28px;font-weight:700}
.thumbs{display:flex;gap:8px;flex-wrap:wrap;margin-top:8px}.thumbs img{height:46px;border-radius:6px;border:1px solid var(--line);background:#fff}
.sticky-cta{position:sticky;bottom:0;margin:0 -2px;padding:10px 0 calc(10px + env(safe-area-inset-bottom,0px));background:linear-gradient(transparent,var(--bg) 30%)}
.modal{position:fixed;inset:0;z-index:50;background:rgba(0,0,0,.55);display:grid;place-items:center;padding:20px}
.modal>div{background:var(--card);border:1px solid var(--line);border-radius:20px;padding:20px;max-width:380px;width:100%;box-shadow:var(--shadow)}
.modal .row{margin-top:16px}
.exgrid{display:grid;grid-template-columns:repeat(auto-fill,minmax(92px,1fr));gap:8px}
.exb{display:flex;flex-direction:column;align-items:center;gap:2px;padding:10px 6px;border-radius:14px;background:var(--card2);color:var(--ink);border:1.5px solid var(--line);font-weight:500}
.exb b{font-size:15px}.exb small{font-size:12px;color:var(--mute)}
.exb.done{border-color:var(--green);background:var(--green2)}.exb.done small{color:var(--green);font-weight:600}
/* sign-up / log-in switch on the first screen */
.authtabs{display:grid;grid-template-columns:1fr 1fr;gap:4px;background:var(--card2);border:1px solid var(--line);border-radius:14px;padding:4px;margin-bottom:14px}
.authtabs button{background:transparent;color:var(--ink);border:0;font-weight:600;padding:11px 8px;border-radius:10px;font-size:15px}
.authtabs button.on{background:var(--green);color:var(--green-ink)}
.newbie{background:var(--green2);border:1px solid var(--green);border-radius:12px;padding:12px 14px;margin-bottom:6px;font-size:14.5px;line-height:1.6}
.timer .ac{margin-left:auto;margin-right:12px;font-size:13px;color:var(--mute);font-variant-numeric:tabular-nums;border:1px solid var(--line);border-radius:999px;padding:2px 9px}
.timer span:first-child{min-width:0;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}