:root {
  --ink: #101935; --ink2: #3B4566; --soft: #6B7491; --line: #E2E6F0; --bg: #F5F7FB; --card: #fff;
  --brand: #4F46E5; --brand2: #4338CA; --teal: #0F9F8C; --gold: #F5A524;
  --good: #15803D; --good-bg: #DCFCE7; --ok: #1D4ED8; --ok-bg: #DBEAFE; --warn: #B45309; --warn-bg: #FEF3C7; --bad: #B91C1C; --bad-bg: #FEE2E2;
  --font: "Inter", "Segoe UI", system-ui, -apple-system, Roboto, sans-serif;
  --mono: "JetBrains Mono", "Cascadia Code", Consolas, "SFMono-Regular", Menlo, monospace;
}
* { box-sizing: border-box; }
body { margin: 0; font: 16px/1.55 var(--font); color: var(--ink); background: var(--bg); min-height: 100vh; display: flex; flex-direction: column; }
a { color: var(--brand); }
button, input, select, textarea { font: inherit; color: inherit; }
code { font-family: var(--mono); font-size: .9em; background: #EEF0F7; padding: 1px 5px; border-radius: 5px; }
.muted { color: var(--soft); }
.small { font-size: 14px; }
.spacer { flex: 1; }
.err { color: var(--bad); font-weight: 600; }
h1 { font-size: 34px; line-height: 1.15; letter-spacing: -.8px; margin: 18px 0 8px; }
h2 { font-size: 21px; letter-spacing: -.3px; margin: 0 0 10px; }
h3 { font-size: 16px; margin: 16px 0 8px; }
.lead { font-size: 18px; color: var(--ink2); max-width: 760px; margin: 0 0 22px; }
.sec { margin: 36px 0 14px; }

/* header */
.top { display: flex; align-items: center; gap: 18px; padding: 14px 28px; background: var(--ink); position: sticky; top: 0; z-index: 5; }
.logo { display: flex; gap: 10px; align-items: center; color: #fff; text-decoration: none; font-size: 19px; font-weight: 600; letter-spacing: -.3px; white-space: nowrap; }
.logo b { color: #5EEAD4; }
.logo img { width: 34px; height: 34px; }
.nav { margin-left: auto; display: flex; gap: 6px; flex-wrap: wrap; }
.nav a { color: #C7CEE3; text-decoration: none; font-weight: 600; font-size: 15px; padding: 6px 12px; border-radius: 8px; }
.nav a:hover, .nav a.on { color: #fff; background: rgba(255, 255, 255, .1); }
main { flex: 1; width: 100%; max-width: 1120px; margin: 0 auto; padding: 10px 24px 40px; }
.foot { text-align: center; color: var(--soft); font-size: 13px; padding: 18px; border-top: 1px solid var(--line); }

/* buttons */
.btn { display: inline-flex; align-items: center; gap: 8px; border: 0; background: var(--brand); color: #fff; font-weight: 700; padding: 11px 20px; border-radius: 11px; cursor: pointer; text-decoration: none; }
.btn:hover { background: var(--brand2); }
.btn.ghost { background: #fff; color: var(--ink); box-shadow: inset 0 0 0 1.5px var(--line); }
.btn.ghost:hover { box-shadow: inset 0 0 0 1.5px #B9C0D6; }
.btn:disabled { opacity: .5; cursor: default; }
.link { border: 0; background: none; color: var(--brand); font-weight: 600; cursor: pointer; padding: 0; }
.link.danger { color: var(--bad); }
.actions { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; margin-top: 16px; }

/* home */
.hero { display: grid; grid-template-columns: 1.6fr 1fr; gap: 28px; align-items: center; margin-top: 18px; }
.hero h1 { font-size: clamp(32px, 5vw, 50px); }
.hero h1 span { background: linear-gradient(90deg, var(--brand), var(--teal)); -webkit-background-clip: text; background-clip: text; color: transparent; }
.cta { display: flex; gap: 10px; flex-wrap: wrap; margin-bottom: 12px; }
.hero-card { background: var(--ink); color: #fff; border-radius: 20px; padding: 24px; display: grid; gap: 14px; }
.hero-card a { color: #5EEAD4; }
.stat b { font-size: 38px; display: block; line-height: 1; }
.stat span { color: #AEB6CF; font-size: 14px; }
.topics { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 12px; }
.topic { background: var(--card); border: 1px solid var(--line); border-top: 4px solid var(--c); border-radius: 14px; padding: 16px; text-decoration: none; color: inherit; display: flex; flex-direction: column; gap: 4px; transition: transform .12s, box-shadow .12s; }
.topic:hover { transform: translateY(-2px); box-shadow: 0 10px 24px rgba(16, 25, 53, .08); }
.ticon { font-size: 24px; }
.topic b { font-size: 17px; }
.tblurb { color: var(--soft); font-size: 14px; flex: 1; }
.tmeta { font-size: 13px; color: var(--ink2); margin-top: 6px; }
.split { display: grid; grid-template-columns: repeat(3, 1fr); gap: 14px; margin-top: 30px; }
.feature { background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 20px; text-decoration: none; color: inherit; display: flex; flex-direction: column; gap: 6px; }
.feature:hover { border-color: #C3C8FA; }
.ficon { font-size: 26px; }
.feature span:last-child { color: var(--ink2); font-size: 15px; }

/* promos */
.promo-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 14px; }
.promo { position: relative; display: flex; flex-direction: column; align-items: flex-start; gap: 10px; text-decoration: none; color: #fff; background: linear-gradient(120deg, #1D2550, #101935); border-radius: 16px; padding: 26px 18px 18px; }
.promo:hover { box-shadow: 0 10px 26px rgba(16, 25, 53, .25); }
.promo-label { position: absolute; top: 8px; left: 18px; font-size: 10px; font-weight: 700; letter-spacing: .14em; text-transform: uppercase; color: #8F9BB3; }
.promo img { width: 60px; height: 60px; border-radius: 13px; object-fit: cover; }
.promo img.book { width: 52px; height: 78px; border-radius: 3px 6px 6px 3px; box-shadow: 0 0 0 1px rgba(255, 255, 255, .35), 2px 3px 10px rgba(0, 0, 0, .45); }
.promo-text { display: flex; flex-direction: column; gap: 3px; flex: 1; }
.promo-kicker { font-size: 11.5px; font-weight: 800; letter-spacing: .08em; text-transform: uppercase; color: #5EEAD4; }
.promo-text strong { font-size: 18px; }
.promo-text span:last-child { color: #C9D1E0; font-size: 14px; }
.promo-cta { background: var(--brand); color: #fff; font-weight: 700; font-size: 14px; border-radius: 10px; padding: 9px 14px; }

/* panels & forms */
.panel { background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 22px; margin-bottom: 16px; }
.panel h3 { margin-top: 0; }
.row-h { display: flex; justify-content: space-between; align-items: baseline; gap: 10px; }
.chips { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 18px; }
.chip-check input { position: absolute; opacity: 0; }
.chip-check span { display: inline-block; border: 1.5px solid var(--line); border-radius: 999px; padding: 7px 14px; font-weight: 600; font-size: 15px; cursor: pointer; background: #fff; }
.chip-check input:checked + span { background: var(--c); border-color: var(--c); color: #fff; }
.chip-check input:focus-visible + span { outline: 3px solid #A5B4FC; }
.grid3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
select { border: 1.5px solid var(--line); border-radius: 10px; padding: 9px 12px; background: #fff; width: 100%; }
.tick { display: flex; gap: 10px; align-items: center; margin-top: 16px; font-weight: 600; }
.tick input { width: 18px; height: 18px; accent-color: var(--brand); }

/* quiz */
.quiz { max-width: 820px; margin: 18px auto 0; }
.qtop { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; font-size: 14px; }
.tag { background: color-mix(in srgb, var(--c) 12%, white); color: var(--c); font-weight: 700; padding: 4px 10px; border-radius: 999px; font-size: 13px; }
.clock { font-weight: 700; font-variant-numeric: tabular-nums; background: #EEF0F7; padding: 3px 10px; border-radius: 8px; }
.clock.low { background: var(--bad-bg); color: var(--bad); }
.bar { height: 6px; background: #E6E9F2; border-radius: 999px; margin: 12px 0 18px; overflow: hidden; }
.bar span { display: block; height: 100%; background: linear-gradient(90deg, var(--brand), var(--teal)); transition: width .3s; }
.question { font-size: 23px; line-height: 1.35; margin: 0 0 14px; }
pre.code { font: 14px/1.5 var(--mono); background: #0F172A; color: #E2E8F0; padding: 14px 16px; border-radius: 12px; overflow-x: auto; white-space: pre; margin: 0 0 16px; }
pre.code.small { font-size: 13px; padding: 10px 12px; }
pre.code.err { background: #2A0F12; color: #FECACA; white-space: pre-wrap; }
.options { display: grid; gap: 10px; }
.opt { display: flex; gap: 12px; align-items: flex-start; text-align: left; background: #fff; border: 1.5px solid var(--line); border-radius: 12px; padding: 13px 16px; cursor: pointer; font-size: 16px; }
.opt:hover:not(:disabled) { border-color: #A5B4FC; background: #F7F7FF; }
.opt .key { flex: none; width: 26px; height: 26px; border-radius: 7px; background: #EEF0F7; display: grid; place-items: center; font-weight: 700; font-size: 13px; }
.opt.right { border-color: var(--good); background: var(--good-bg); }
.opt.wrong { border-color: var(--bad); background: var(--bad-bg); }
.opt:disabled { cursor: default; }
.explain { margin-top: 14px; padding: 14px 16px; border-radius: 12px; }
.explain.good { background: var(--good-bg); }
.explain.bad { background: var(--bad-bg); }
.qnav { margin-top: 22px; }

/* report */
.score-card { display: flex; gap: 26px; align-items: center; background: var(--card); border: 1px solid var(--line); border-radius: 20px; padding: 24px; margin-top: 18px; }
.score-card h1 { margin: 2px 0 6px; }
.kicker { text-transform: uppercase; letter-spacing: .1em; font-size: 12px; font-weight: 700; color: var(--soft); margin: 0; }
.ring { --c: var(--brand); width: 130px; height: 130px; flex: none; border-radius: 50%; display: grid; place-items: center;
  background: conic-gradient(var(--c) calc(var(--p) * 1%), #E6E9F2 0); }
.ring b { width: 100px; height: 100px; border-radius: 50%; background: #fff; display: grid; place-items: center; font-size: 28px; }
.good .ring { --c: var(--good); } .ok .ring { --c: var(--ok); } .warn .ring { --c: var(--warn); } .bad .ring { --c: var(--bad); }
.bars { background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 10px 20px; }
.brow { display: grid; grid-template-columns: 230px 1fr 50px 110px; gap: 12px; align-items: center; padding: 9px 0; border-bottom: 1px solid var(--line); }
.brow:last-child { border-bottom: 0; }
.bname { font-weight: 600; }
.btrack { height: 10px; background: #E6E9F2; border-radius: 999px; overflow: hidden; }
.bfill { display: block; height: 100%; border-radius: 999px; }
.bfill.good { background: var(--good); } .bfill.ok { background: var(--ok); } .bfill.warn { background: var(--gold); } .bfill.bad { background: var(--bad); }
.bval { font-weight: 700; text-align: right; }
.pill { display: inline-block; font-size: 12.5px; font-weight: 700; border-radius: 999px; padding: 2px 9px; white-space: nowrap; }
.pill.good { background: var(--good-bg); color: var(--good); } .pill.ok { background: var(--ok-bg); color: var(--ok); }
.pill.warn { background: var(--warn-bg); color: var(--warn); } .pill.bad { background: var(--bad-bg); color: var(--bad); }
.cols2 { display: grid; grid-template-columns: 1.3fr 1fr; gap: 16px; margin-top: 18px; }
.cols2.tight { grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 6px; }
.focus { padding-left: 20px; }
.focus li { margin-bottom: 14px; }
.focus p { margin: 4px 0; color: var(--ink2); font-size: 15px; }
.strong { list-style: none; padding: 0; }
.strong li { padding: 6px 0; border-bottom: 1px solid var(--line); display: flex; gap: 8px; align-items: center; }
.strong li .pill { margin-left: auto; }
.review { display: grid; gap: 8px; }
.rv { background: var(--card); border: 1px solid var(--line); border-left: 4px solid var(--good); border-radius: 10px; padding: 10px 14px; }
.rv.no { border-left-color: var(--bad); }
.rv summary { cursor: pointer; display: flex; gap: 8px; }
.rv .mark { font-weight: 800; color: var(--good); }
.rv.no .mark { color: var(--bad); }
.rv p { margin: 8px 0 0; }

/* progress */
.tbl { width: 100%; border-collapse: collapse; }
.tbl th, .tbl td { text-align: left; padding: 9px 10px; border-bottom: 1px solid var(--line); }
.tbl th { font-size: 13px; color: var(--soft); font-weight: 700; }
.tbl.small td, .tbl.small th { padding: 5px 8px; font-size: 13.5px; }
.tblwrap { overflow-x: auto; }
.spark { display: inline-flex; gap: 3px; align-items: flex-end; height: 26px; }
.spark i { width: 8px; border-radius: 2px; display: block; }
.spark i.good { background: var(--good); } .spark i.ok { background: var(--ok); } .spark i.warn { background: var(--gold); } .spark i.bad { background: var(--bad); }
.hist { list-style: none; padding: 0; margin: 0; }
.hist li { display: flex; gap: 12px; align-items: center; padding: 9px 0; border-bottom: 1px solid var(--line); }
.hist li span:nth-child(2) { color: var(--soft); flex: 1; font-size: 14px; }

/* coding */
.filters { display: flex; gap: 10px; align-items: center; margin-bottom: 14px; flex-wrap: wrap; }
.filters select { width: auto; }
.clist { display: grid; gap: 8px; }
.crow { display: grid; grid-template-columns: 30px 1fr auto 80px; gap: 12px; align-items: center; background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 12px 16px; text-decoration: none; color: inherit; }
.crow:hover { border-color: #A5B4FC; }
.cname { display: flex; flex-direction: column; }
.cname .muted { font-size: 13px; }
.langs { display: flex; gap: 6px; }
.lang { font-size: 12px; font-weight: 700; border-radius: 6px; padding: 2px 8px; background: #EEF0F7; }
.lang.python { background: #FEF3C7; color: #92400E; } .lang.javascript { background: #FEF9C3; color: #854D0E; } .lang.sql { background: #DBEAFE; color: #1E40AF; }
.lvl { font-size: 12.5px; font-weight: 800; text-align: center; border-radius: 999px; padding: 3px 10px; }
.lvl.easy { background: var(--good-bg); color: var(--good); } .lvl.medium { background: var(--warn-bg); color: var(--warn); } .lvl.hard { background: var(--bad-bg); color: var(--bad); }
.ide { display: grid; grid-template-columns: minmax(300px, 0.9fr) 1.2fr; gap: 18px; margin-top: 14px; align-items: start; }
.problem { background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 20px; }
.problem h1 { font-size: 26px; margin: 10px 0 6px; }
.problem details { margin: 6px 0; }
.problem summary { cursor: pointer; font-weight: 600; font-size: 14px; }
.editor-wrap { position: sticky; top: 76px; }
.etop { display: flex; gap: 14px; align-items: center; margin-bottom: 8px; }
.etop select { width: auto; }
.editor { display: flex; background: #0F172A; border-radius: 14px; overflow: hidden; height: 360px; }
.gutter { margin: 0; padding: 14px 8px 14px 12px; color: #64748B; font: 14px/1.5 var(--mono); text-align: right; user-select: none; overflow: hidden; min-width: 44px; background: #0B1222; }
.editor textarea { flex: 1; border: 0; outline: none; resize: none; background: transparent; color: #E2E8F0; font: 14px/1.5 var(--mono); padding: 14px; white-space: pre; overflow: auto; tab-size: 4; caret-color: #5EEAD4; }
.out { margin-top: 14px; }
.verdict { font-weight: 800; padding: 10px 14px; border-radius: 10px; margin-bottom: 8px; }
.verdict.good { background: var(--good-bg); color: var(--good); }
.verdict.bad { background: var(--bad-bg); color: var(--bad); }
.tests { display: grid; gap: 6px; }
.test { background: var(--card); border: 1px solid var(--line); border-left: 4px solid var(--good); border-radius: 10px; padding: 8px 12px; }
.test.no { border-left-color: var(--bad); }
.test summary { cursor: pointer; font-weight: 600; }
.test pre { margin: 8px 0 2px; }
.test h4 { margin: 8px 0 4px; font-size: 13px; color: var(--soft); }
.prose { max-width: 780px; }
.prose li { margin: 6px 0; }

@media (max-width: 900px) {
  .hero, .ide, .cols2, .split, .grid3 { grid-template-columns: 1fr; }
  .editor-wrap { position: static; }
  .brow { grid-template-columns: 1fr 50px; }
  .brow .btrack { grid-column: 1 / -1; grid-row: 2; }
  .brow .pill { display: none; }
}
@media (max-width: 640px) {
  .top { padding: 12px 14px; flex-wrap: wrap; }
  .nav { margin-left: 0; width: 100%; }
  .nav a { padding: 5px 8px; font-size: 14px; }
  main { padding: 6px 14px 30px; }
  h1 { font-size: 28px; }
  .score-card { flex-direction: column; text-align: center; }
  .crow { grid-template-columns: 24px 1fr 64px; }
  .crow .langs { display: none; }
  .question { font-size: 20px; }
}
@media print {
  .top, .foot, .noprint, #drill { display: none !important; }
  body { background: #fff; }
  .rv { break-inside: avoid; }
  details { display: block; }
}

/* keep the editor column inside the page */
.ide > * { min-width: 0; }
.test pre, .problem pre.code.small { white-space: pre-wrap; word-break: break-word; }