:root {
  --bg: #f5f7fb; --card: #ffffff; --text: #1d2433; --muted: #667085; --line: #e3e8ef;
  --brand: #1f6f8b; --brand-2: #e8f3f7; --good: #1a7f4b; --good-bg: #e6f6ed; --ok: #946200; --ok-bg: #fff4d6;
  --weak: #b42318; --weak-bg: #fde8e7; --state: #6941c6; --state-bg: #f1ebff;
}
@media (prefers-color-scheme: dark) {
  :root { --bg: #11161f; --card: #1a2130; --text: #e6e9ef; --muted: #98a2b3; --line: #2b3445;
    --brand: #5cb6d6; --brand-2: #1d3340; --good: #6fd39c; --good-bg: #173426; --ok: #f2c14e; --ok-bg: #3a2f12;
    --weak: #f59a93; --weak-bg: #3d1d1b; --state: #b9a0f5; --state-bg: #2a2142; }
}
* { box-sizing: border-box; }
body { margin: 0; font: 16px/1.55 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif; background: var(--bg); color: var(--text); }
a { color: var(--brand); }
h1 { font-size: 1.7rem; margin: .4rem 0 .6rem; } h2 { font-size: 1.2rem; margin: 0 0 .6rem; } h3 { font-size: 1.02rem; margin: .8rem 0 .4rem; }
.top { display: flex; flex-wrap: wrap; align-items: center; gap: .5rem 1.2rem; padding: .7rem 1.2rem; background: var(--card); border-bottom: 1px solid var(--line); position: sticky; top: 0; z-index: 5; }
.brand { font-weight: 700; text-decoration: none; color: var(--text); font-size: 1.1rem; }
.top nav { display: flex; flex-wrap: wrap; gap: .2rem .9rem; flex: 1; }
.top nav a { text-decoration: none; font-weight: 500; }
.who { color: var(--muted); font-size: .9rem; }
main { max-width: 1100px; margin: 0 auto; padding: 1.2rem 16px 3rem; }
footer { text-align: center; color: var(--muted); font-size: .8rem; padding: 1rem 16px 2rem; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 1rem 1.2rem; margin: 0 0 1rem; }
.grid2 { display: grid; grid-template-columns: repeat(auto-fit, minmax(320px, 1fr)); gap: 1rem; }
.grid2 > .card { margin: 0; }
.layout2 { display: grid; grid-template-columns: minmax(0, 1fr) 300px; gap: 1rem; align-items: start; }
@media (max-width: 860px) { .layout2 { grid-template-columns: 1fr; } }
.lead { color: var(--muted); font-size: 1.05rem; max-width: 70ch; }
.muted { color: var(--muted); } .small { font-size: .85rem; }
.crumbs { margin: 0; font-size: .9rem; color: var(--muted); }
.list { margin: .2rem 0 .6rem; padding-left: 1.1rem; } .list li { margin: .25rem 0; }
.links { list-style: none; padding: 0; margin: 0; } .links li { padding: .45rem 0; border-bottom: 1px solid var(--line); } .links li:last-child { border: 0; }
.btn { display: inline-block; background: var(--brand); color: #fff; border: 0; border-radius: 8px; padding: .55rem 1rem; font: inherit; font-weight: 600; cursor: pointer; text-decoration: none; }
.btn:hover { filter: brightness(1.08); } .btn:disabled { opacity: .5; cursor: not-allowed; }
.btn.secondary { background: var(--brand-2); color: var(--brand); }
.btn.small { padding: .3rem .65rem; font-size: .85rem; } .btn.big { padding: .75rem 1.4rem; font-size: 1.05rem; }
.linkbtn { background: none; border: 0; color: var(--brand); cursor: pointer; font: inherit; padding: 0; text-decoration: underline; font-size: .85rem; }
.linkbtn.danger { color: var(--weak); }
form.inline { display: inline; }
.badge { display: inline-block; white-space: nowrap; font-size: .75rem; font-weight: 600; padding: .05rem .5rem; border-radius: 99px; background: var(--brand-2); color: var(--brand); vertical-align: middle; }
.badge.good { background: var(--good-bg); color: var(--good); } .badge.ok { background: var(--ok-bg); color: var(--ok); }
.badge.weak { background: var(--weak-bg); color: var(--weak); } .badge.muted { background: var(--bg); color: var(--muted); border: 1px solid var(--line); }
.badge.state { background: var(--state-bg); color: var(--state); }
.flash { background: var(--brand-2); border: 1px solid var(--brand); color: var(--text); padding: .6rem .9rem; border-radius: 8px; margin-bottom: 1rem; }
.flash.error { background: var(--weak-bg); border-color: var(--weak); }
.tbl { width: 100%; border-collapse: collapse; font-size: .95rem; } .tbl th, .tbl td { text-align: left; padding: .45rem .5rem; border-bottom: 1px solid var(--line); vertical-align: top; }
.tbl th { color: var(--muted); font-weight: 600; font-size: .85rem; } .tbl.compact td, .tbl.compact th { padding: .3rem .4rem; }
.card { overflow-x: auto; }
input, select, textarea { font: inherit; color: var(--text); background: var(--bg); border: 1px solid var(--line); border-radius: 7px; padding: .45rem .6rem; max-width: 100%; }
textarea { width: 100%; } .mono { font-family: ui-monospace, Consolas, monospace; font-size: .9rem; }
label.block { display: block; margin: .6rem 0; } label.block input { width: 100%; display: block; margin-top: .2rem; }
.row { display: flex; flex-wrap: wrap; gap: .8rem 1rem; align-items: end; margin: .6rem 0; } .row label { display: flex; flex-direction: column; gap: .2rem; font-size: .9rem; }
label.check { display: block; margin: .3rem 0; } .row label.check { flex-direction: row; align-items: center; gap: .4rem; }
fieldset { border: 1px solid var(--line); border-radius: 10px; margin: .6rem 0; padding: .4rem .9rem .7rem; } legend { font-weight: 600; padding: 0 .3rem; }
.grow { flex: 1; width: 100%; }
.login { max-width: 420px; margin: 3rem auto; }
.stats { display: flex; gap: 1rem; flex-wrap: wrap; margin-bottom: 1rem; }
.stat { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: .7rem 1.1rem; color: var(--muted); min-width: 120px; } .stat b { display: block; font-size: 1.6rem; color: var(--text); }
.stage.done { border-color: var(--good); } .stagehead { display: flex; gap: .8rem; align-items: center; margin-bottom: .4rem; } .stagehead h2 { margin: 0; }
.stagenum { width: 2.2rem; height: 2.2rem; border-radius: 50%; background: var(--brand); color: #fff; display: grid; place-items: center; font-weight: 700; flex: none; }
.stage.done .stagenum { background: var(--good); }
.note { line-height: 1.65; } .note h2 { margin-top: 1.4rem; font-size: 1.25rem; } .note table, .prompt table, .explain table { border-collapse: collapse; margin: .6rem 0; }
.note th, .note td, .prompt th, .prompt td, .explain th, .explain td { border: 1px solid var(--line); padding: .3rem .6rem; }
.note th, .prompt th { background: var(--bg); }
.note code, .prompt code { background: var(--bg); padding: 0 .3rem; border-radius: 4px; }
.q { margin-bottom: .9rem; } .qhead { display: flex; gap: .6rem; align-items: center; margin-bottom: .3rem; }
.qnum { background: var(--brand); color: #fff; font-weight: 700; border-radius: 6px; padding: 0 .55rem; }
.prompt p:first-child { margin-top: 0; }
.choice { display: flex; gap: .55rem; align-items: flex-start; padding: .45rem .6rem; border: 1px solid var(--line); border-radius: 8px; margin: .35rem 0; cursor: pointer; }
.choice:hover { border-color: var(--brand); } .choice input[type=radio] { margin-top: .3rem; } .choice p { margin: 0; }
.numeric input { width: 12rem; }
.review.right { border-left: 5px solid var(--good); } .review.wrong { border-left: 5px solid var(--weak); } .review.self { border-left: 5px solid var(--ok); }
.verdict { margin-left: auto; font-weight: 600; }
.explain { background: var(--bg); border-radius: 8px; padding: .5rem .8rem; margin-top: .6rem; } .explain p { margin: .3rem 0; }
.scorecard { display: flex; gap: 1.5rem; align-items: center; flex-wrap: wrap; }
.bigscore { font-size: 2.4rem; font-weight: 800; text-align: center; min-width: 140px; } .bigscore small { display: block; font-size: 1rem; font-weight: 600; }
.bigscore.good { color: var(--good); } .bigscore.ok { color: var(--ok); } .bigscore.weak { color: var(--weak); }
.timer { position: sticky; top: 3.6rem; z-index: 4; display: inline-block; background: var(--card); border: 2px solid var(--brand); border-radius: 99px; padding: .3rem 1rem; font-weight: 700; margin-bottom: .8rem; }
.timer.low { border-color: var(--weak); color: var(--weak); }
.qlist li { margin: .5rem 0; }
[hidden] { display: none !important; }
/* ---------- chat ---------- */
.navbadge { margin-left: .3rem; }
.chatwrap { display: grid; grid-template-columns: 220px minmax(0, 1fr); gap: 1rem; align-items: start; }
@media (max-width: 760px) { .chatwrap { grid-template-columns: 1fr; } .chanlist { display: flex; flex-wrap: wrap; gap: .3rem .8rem; } .chanlist h3 { width: 100%; margin: 0; } }
.chanlist .chan { display: block; padding: .35rem .5rem; border-radius: 7px; text-decoration: none; color: var(--text); }
.chanlist .chan.active { background: var(--brand-2); color: var(--brand); font-weight: 600; }
.chat { display: flex; flex-direction: column; height: calc(100vh - 170px); min-height: 420px; padding: 0; overflow: hidden; }
.chathead { padding: .7rem 1rem; border-bottom: 1px solid var(--line); }
.msgs { flex: 1; overflow-y: auto; padding: .8rem 1rem; display: flex; flex-direction: column; gap: .55rem; }
.msg { max-width: 80%; background: var(--bg); border: 1px solid var(--line); border-radius: 12px; padding: .45rem .75rem; align-self: flex-start; }
.msg.mine { align-self: flex-end; background: var(--brand-2); }
.msg.mentor { border-color: var(--state); }
.msg.deleted .msgbody { color: var(--muted); font-style: italic; }
.msghead { font-size: .85rem; display: flex; gap: .3rem; align-items: baseline; flex-wrap: wrap; }
.msgdel { margin-left: auto; font-size: .75rem; }
.msgbody { overflow-wrap: anywhere; }
.attachment { display: inline-block; margin-top: .35rem; } .attachment img { max-width: 260px; max-height: 220px; border-radius: 8px; display: block; }
.composer { border-top: 1px solid var(--line); padding: .7rem 1rem; }
.composer textarea { resize: vertical; }
.composer-row { display: flex; align-items: center; gap: .7rem; margin-top: .4rem; } .composer-row .btn { margin-left: auto; }
.attach { cursor: pointer; color: var(--brand); font-weight: 600; } .attach input { display: none; }
.composer p { margin: .4rem 0 0; }
.welcome { border-left: 5px solid var(--brand); }
.welcome h2:first-child { margin-top: 0; }