/* Base layer shared by every design direction: layout, components and maths/figure handling.
   Directions (static/designs/*.css) set the custom properties below for light and dark mode
   and add their own personality on top. Nothing here hard-codes a colour or a font. */

:root {
  --bg: #fff; --bg-2: #f6f7f9; --surface: #fff; --surface-2: #f3f4f6; --text: #111;
  --muted: #5b6270; --border: #e3e5e8; --border-strong: #c9cdd3; --accent: #2457d6;
  --accent-strong: #1c45ad; --on-accent: #fff; --accent-soft: #e8eefc; --accent-2: #0f8b7d;
  --good: #16794a; --good-soft: #e3f4ea; --bad: #b4232a; --bad-soft: #fbe7e8;
  --free: #16794a; --free-soft: #e3f4ea; --link: var(--accent); --focus: var(--accent);
  --star: var(--accent); --star-off: var(--border-strong);
  --font-body: system-ui, sans-serif; --font-ui: var(--font-body); --font-heading: var(--font-ui);
  --font-mono: ui-monospace, monospace; --font-num: var(--font-ui);
  --fs-body: 17px; --lh-body: 1.65; --measure: 70ch; --wrap: 1180px;
  --radius: 8px; --radius-sm: 6px; --radius-lg: 14px; --border-w: 1px;
  --shadow: 0 1px 2px rgba(0,0,0,.05); --shadow-lg: 0 8px 30px rgba(0,0,0,.08);
  --heading-weight: 700; --heading-tracking: -0.01em; --title-size: clamp(1.7rem, 1.2rem + 1.6vw, 2.4rem);
  --eyebrow-size: 0.95rem;
  --header-bg: var(--bg); --header-border: var(--border); --btn-radius: var(--radius-sm);
  --toolkit-bg: var(--surface-2); --toolkit-border: var(--border);
  --answer-bg: var(--surface); --fig-bg: var(--bg);
  color-scheme: light;
}
:root[data-theme="dark"] { color-scheme: dark; }

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; text-size-adjust: 100%; }
body {
  margin: 0; background: var(--bg); color: var(--text);
  font: 400 var(--fs-body)/var(--lh-body) var(--font-body);
  -webkit-font-smoothing: antialiased; text-rendering: optimizeLegibility;
  min-height: 100vh; display: flex; flex-direction: column;
}
.site-main { flex: 1; }
img, svg { max-width: 100%; }
a { color: var(--link); text-decoration-thickness: 1px; text-underline-offset: 0.18em; }
a:hover { color: var(--accent-strong); }
:focus-visible { outline: 2px solid var(--focus); outline-offset: 2px; border-radius: 2px; }
h1, h2, h3 { font-family: var(--font-heading); font-weight: var(--heading-weight); letter-spacing: var(--heading-tracking); line-height: 1.2; margin: 0; }
p { margin: 0 0 0.9em; }
.wrap { width: 100%; max-width: var(--wrap); margin: 0 auto; padding: 0 24px; }
.skip-link { position: absolute; left: -999px; top: 8px; background: var(--surface); padding: 8px 12px; z-index: 100; }
.skip-link:focus { left: 8px; }

/* ---- header ---------------------------------------------------------------------------- */
.site-header { background: var(--header-bg); border-bottom: var(--border-w) solid var(--header-border); position: sticky; top: 0; z-index: 20; }
.header-inner { display: flex; align-items: center; gap: 28px; height: 64px; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--text); font-family: var(--font-heading); font-weight: 700; font-size: 1.12rem; letter-spacing: -0.01em; }
.brand-mark svg { display: block; }
.brand-mark .bm-bg { fill: var(--accent); }
/* Double-struck Ω, full cut: the paths are copied from brand/mark.svg (built by brand/build.mjs). */
.brand-mark .bm-o { fill: none; stroke: var(--on-accent); stroke-width: 24; stroke-linecap: square; stroke-linejoin: miter; }
.site-nav { display: flex; gap: 22px; font-family: var(--font-ui); font-size: 0.95rem; }
.site-nav a { color: var(--muted); text-decoration: none; padding: 6px 0; border-bottom: 2px solid transparent; }
.site-nav a:hover { color: var(--text); }
.site-nav a[aria-current="page"] { color: var(--text); border-bottom-color: var(--accent); }
.header-actions { margin-left: auto; display: flex; align-items: center; gap: 10px; }
.theme-toggle { background: none; border: var(--border-w) solid var(--border); color: var(--muted); width: 36px; height: 36px; border-radius: var(--btn-radius); display: grid; place-items: center; cursor: pointer; }
.theme-toggle:hover { color: var(--text); border-color: var(--border-strong); }
.theme-toggle svg { fill: none; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; }
.theme-toggle .icon-moon { display: none; }
:root[data-theme="dark"] .theme-toggle .icon-sun { display: none; }
:root[data-theme="dark"] .theme-toggle .icon-moon { display: block; }

/* ---- buttons, badges, difficulty -------------------------------------------------------- */
.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; font: 600 0.95rem/1 var(--font-ui); padding: 11px 18px; border-radius: var(--btn-radius); border: var(--border-w) solid transparent; text-decoration: none; cursor: pointer; white-space: nowrap; transition: background .15s, border-color .15s, color .15s; }
.btn-sm { padding: 8px 13px; font-size: 0.88rem; }
.btn-lg { padding: 14px 22px; font-size: 1rem; }
.btn-block { width: 100%; }
.btn-primary { background: var(--accent); color: var(--on-accent); }
.btn-primary:hover { background: var(--accent-strong); color: var(--on-accent); }
.btn-secondary { background: var(--surface); color: var(--text); border-color: var(--border-strong); }
.btn-secondary:hover { border-color: var(--text); color: var(--text); }
.btn-ghost { background: transparent; color: var(--text); border-color: transparent; }
.btn-ghost:hover { background: var(--surface-2); color: var(--text); }
.btn-good { background: var(--good-soft); color: var(--good); border-color: transparent; }
.btn-link { background: none; border: none; color: var(--link); padding: 4px 0; font-weight: 500; text-decoration: underline; text-underline-offset: 0.2em; }
.badge { display: inline-flex; align-items: center; gap: 4px; font: 600 0.72rem/1 var(--font-ui); letter-spacing: 0.02em; padding: 4px 8px; border-radius: 999px; white-space: nowrap; }
.badge-free { background: var(--free-soft); color: var(--free); }
.badge-pro { background: var(--accent-soft); color: var(--accent-strong); }
.badge-lock { color: var(--muted); padding: 4px; }
.badge-lock svg { fill: none; stroke: currentColor; stroke-width: 1.4; }
.difficulty { display: inline-flex; align-items: center; gap: 6px; font: 500 0.82rem/1 var(--font-ui); color: var(--muted); white-space: nowrap; }
.difficulty .stars { color: var(--star); letter-spacing: 0.08em; font-size: 0.9em; }
.difficulty .stars .off { color: var(--star-off); }
.eyebrow { font: 600 var(--eyebrow-size)/1.2 var(--font-ui); color: var(--accent-strong); margin: 0 0 10px; }
.lede { font-size: 1.08rem; color: var(--muted); max-width: 62ch; }
.page-head { padding: 40px 0 28px; }
.page-head.centered { text-align: center; }
.page-head.centered .lede { margin: 0 auto; }
.page-title { font-size: var(--title-size); margin-bottom: 12px; }
.breadcrumbs { font: 500 0.85rem/1.4 var(--font-ui); color: var(--muted); padding-top: 26px; display: flex; flex-wrap: wrap; gap: 6px; }
.breadcrumbs a { color: var(--muted); text-decoration: none; }
.breadcrumbs a:hover { color: var(--text); text-decoration: underline; }
.breadcrumbs .sep { opacity: .5; }

/* ---- prose: statements, solutions, toolkits --------------------------------------------- */
.prose { max-width: var(--measure); }
.prose p { margin: 0 0 0.85em; }
.prose ul, .prose ol { margin: 0 0 0.9em; padding-left: 1.4em; }
.prose li { margin: 0.25em 0; }
.prose li > ul, .prose li > ol { margin: 0.3em 0; }
.prose em { font-style: italic; }
.prose strong { font-weight: 650; }
.prose .center { text-align: center; }
.prose .center > div, .prose .center .table-wrap { display: flex; justify-content: center; }
.math-display { overflow-x: auto; overflow-y: hidden; margin: 0.7em 0 0.9em; padding: 2px 0; -webkit-overflow-scrolling: touch; }
.math-display .katex-display { margin: 0; }
.katex { font-size: 1.07em; }
.katex-display > .katex { white-space: nowrap; }
.boxed-prose { border: 1.5px solid currentColor; padding: 0.7em 1em; margin: 0.9em auto; width: fit-content; max-width: 100%; text-align: center; border-radius: 2px; }
.boxed-prose p:last-child { margin: 0; }
.nowrap { white-space: nowrap; }
.table-wrap { overflow-x: auto; margin: 0.6em 0 1em; }
.prose table { border-collapse: collapse; font-size: 0.95em; font-variant-numeric: tabular-nums; }
.prose th, .prose td { padding: 6px 12px; vertical-align: middle; }
.prose thead th { border-bottom: var(--border-w) solid var(--border-strong); font-weight: 600; }
.prose td.rule-r, .prose th.rule-r { border-right: var(--border-w) solid var(--border-strong); }
.prose tr.rule-b td { border-bottom: var(--border-w) solid var(--border-strong); }
.a-left { text-align: left; } .a-center { text-align: center; } .a-right { text-align: right; }
.figure { margin: 0.4em 0 1.2em; text-align: center; color: var(--text); }
.figure svg.fig { height: auto; max-width: min(100%, 520px); }
code { font-family: var(--font-mono); font-size: 0.92em; }

/* ---- problem page ----------------------------------------------------------------------- */
.problem-layout { display: grid; grid-template-columns: minmax(0, 1fr) 280px; gap: 56px; align-items: start; padding-bottom: 64px; }
.problem-head { margin: 18px 0 22px; }
.problem-meta { display: flex; flex-wrap: wrap; align-items: center; gap: 12px; margin-bottom: 10px; }
.problem-num { font: 600 0.85rem/1 var(--font-num); color: var(--muted); letter-spacing: 0.02em; }
.meta-note { font: 500 0.82rem/1 var(--font-ui); color: var(--muted); }
.problem-title { font-size: var(--title-size); }
.statement { font-size: 1.04em; }
.answer-box { background: var(--answer-bg); border: var(--border-w) solid var(--border); border-radius: var(--radius); padding: 18px 20px; margin: 24px 0; max-width: var(--measure); }
.answer-box.compact { padding: 14px 16px; margin: 14px 0; }
.answer-prompt { display: block; font: 600 0.88rem/1.3 var(--font-ui); margin: 0 0 10px; color: var(--text); }
.answer-row { display: flex; gap: 10px; flex-wrap: wrap; }
.answer-input { flex: 1 1 180px; min-width: 0; font: 500 1rem/1.2 var(--font-mono); color: var(--text); background: var(--bg); border: var(--border-w) solid var(--border-strong); border-radius: var(--btn-radius); padding: 11px 13px; }
.answer-input::placeholder { color: var(--muted); opacity: .7; font-family: var(--font-ui); }
.answer-input:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.answer-actions { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-top: 10px; flex-wrap: wrap; }
.answer-hint { font: 400 0.82rem/1.3 var(--font-ui); color: var(--muted); }
.answer-reveal { margin-top: 14px; padding-top: 14px; border-top: var(--border-w) dashed var(--border); }
.answer-value { display: flex; gap: 14px; align-items: baseline; flex-wrap: wrap; }
.answer-label { font: 600 0.88rem/1 var(--font-ui); color: var(--muted); }
.answer-body p:last-child { margin-bottom: 0; }
.self-mark { display: flex; align-items: center; gap: 10px; margin-top: 12px; font: 500 0.88rem/1 var(--font-ui); color: var(--muted); flex-wrap: wrap; }
.answer-feedback { margin-top: 10px; font: 600 0.9rem/1.3 var(--font-ui); }
details.solution { border: var(--border-w) solid var(--border); border-radius: var(--radius); margin: 18px 0; max-width: var(--measure); background: var(--surface); }
details.solution > summary { list-style: none; cursor: pointer; padding: 14px 20px; display: flex; align-items: baseline; gap: 12px; font: 600 1rem/1.2 var(--font-ui); }
details.solution > summary::-webkit-details-marker { display: none; }
details.solution > summary::before { content: "+"; font: 600 1.1rem/1 var(--font-mono); color: var(--accent); width: 1ch; }
details.solution[open] > summary::before { content: "−"; }
.summary-hint { font-weight: 400; font-size: .88rem; color: var(--muted); }
details.solution[open] .summary-hint { display: none; }
.solution-body { padding: 4px 20px 16px; border-top: var(--border-w) solid var(--border); padding-top: 16px; max-width: none; }
.variations { margin-top: 44px; }
.variations-title { font-size: 1.35rem; margin-bottom: 6px; }
.variations-lede { color: var(--muted); font-size: .95rem; }
.variation { border-left: 3px solid var(--accent-2); padding: 4px 0 4px 20px; margin: 26px 0; }
.variation-num { font: 700 0.85rem/1 var(--font-num); color: var(--accent-2); letter-spacing: .02em; }
.variation-head { margin-bottom: 10px; }
.variation details.solution, .variation .answer-box { max-width: calc(var(--measure) - 23px); }
.report-row { margin: 28px 0 0; font-size: .88rem; }
.report-row .btn-link { color: var(--muted); font-size: .85rem; }
.pager { display: flex; justify-content: space-between; gap: 16px; margin-top: 36px; padding-top: 22px; border-top: var(--border-w) solid var(--border); }
.pager a { display: flex; flex-direction: column; gap: 4px; text-decoration: none; max-width: 48%; color: var(--text); }
.pager a:hover .pager-title { color: var(--accent-strong); }
.pager-next { text-align: right; margin-left: auto; }
.pager-dir { font: 500 .85rem/1 var(--font-ui); color: var(--muted); }
.pager-title { font: 600 .98rem/1.3 var(--font-ui); }
.problem-aside, .section-aside { position: sticky; top: 88px; padding-top: 30px; }
.aside-card { border: var(--border-w) solid var(--border); border-radius: var(--radius); padding: 18px; background: var(--surface); font-family: var(--font-ui); }
.aside-eyebrow { font: 500 .85rem/1 var(--font-ui); color: var(--muted); margin-bottom: 8px; }
.aside-title { display: block; font: 700 1rem/1.3 var(--font-heading); color: var(--text); text-decoration: none; margin-bottom: 6px; }
.aside-toolkit { font-size: .85rem; font-weight: 600; }
.aside-list { list-style: none; margin: 14px 0 0; padding: 0; font-size: .88rem; max-height: 60vh; overflow: auto; }
.aside-list a { display: flex; gap: 10px; padding: 6px 8px; border-radius: var(--radius-sm); text-decoration: none; color: var(--muted); align-items: baseline; }
.aside-list a:hover { background: var(--surface-2); color: var(--text); }
.aside-list .current a { background: var(--accent-soft); color: var(--text); font-weight: 600; }
.aside-list .num { font-family: var(--font-num); font-size: .8rem; min-width: 3.2em; color: var(--muted); }
.aside-list .t { flex: 1; }
.dot-free { width: 7px; height: 7px; border-radius: 50%; background: var(--free); flex: none; align-self: center; }

/* ---- section page ----------------------------------------------------------------------- */
.section-layout { display: grid; grid-template-columns: minmax(0, 1fr) 280px; gap: 56px; align-items: start; padding-bottom: 64px; }
.toolkit { background: var(--toolkit-bg); border: var(--border-w) solid var(--toolkit-border); border-radius: var(--radius); padding: 20px 24px 8px; margin: 4px 0 34px; }
.toolkit-title { font: 700 1rem/1.2 var(--font-ui); color: var(--accent-strong); margin-bottom: 14px; }
.toolkit .prose { max-width: none; }
.list-title { font-size: 1.25rem; margin-bottom: 12px; }
.problem-list { list-style: none; margin: 0; padding: 0; border-top: var(--border-w) solid var(--border); }
.problem-row a { display: grid; grid-template-columns: 18px 3.6em minmax(0, 1fr) auto 64px; align-items: center; gap: 14px; padding: 14px 8px; border-bottom: var(--border-w) solid var(--border); text-decoration: none; color: var(--text); }
.problem-row a:hover { background: var(--surface-2); }
.problem-row .num { font: 600 .85rem/1 var(--font-num); color: var(--muted); }
.problem-row .title { font: 600 1rem/1.35 var(--font-ui); }
.problem-row .badge { justify-self: end; }
.nvar { font: 500 .75rem/1 var(--font-ui); color: var(--muted); margin-left: 10px; white-space: nowrap; }
.status { display: inline-block; flex: none; width: 14px; height: 14px; border-radius: 50%; border: 1.5px solid var(--border-strong); vertical-align: -2px; position: relative; }
.status.seen { border-style: dashed; border-color: var(--muted); }
.status.attempted { border-color: var(--accent); background: linear-gradient(90deg, var(--accent-soft) 50%, transparent 50%); }
.status.solved { border-color: var(--good); background: var(--good); }
.status.solved::after { content: ""; position: absolute; left: 4px; top: 1px; width: 3px; height: 7px; border: solid var(--bg); border-width: 0 1.6px 1.6px 0; transform: rotate(45deg); }
.progress { display: flex; align-items: center; gap: 12px; margin-top: 18px; font: 500 .82rem/1 var(--font-ui); color: var(--muted); }
.progress-bar { flex: 0 1 220px; height: 6px; border-radius: 99px; background: var(--surface-2); overflow: hidden; border: var(--border-w) solid var(--border); }
.progress-bar span { display: block; height: 100%; background: var(--accent); }

/* ---- course page ------------------------------------------------------------------------ */
.course-layout { padding-bottom: 64px; }
.part-index { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 28px; }
.part-index a { display: inline-flex; gap: 8px; align-items: baseline; padding: 8px 12px; border: var(--border-w) solid var(--border); border-radius: 999px; text-decoration: none; color: var(--text); font: 500 .88rem/1 var(--font-ui); background: var(--surface); }
.part-index a:hover { border-color: var(--accent); }
.pi-num { font-family: var(--font-num); color: var(--accent-strong); font-weight: 700; }
.part { padding: 34px 0 10px; border-top: var(--border-w) solid var(--border); }
.part-head { margin-bottom: 20px; }
.part-title { font-size: 1.7rem; margin-bottom: 8px; }
.part-intro { color: var(--muted); max-width: 70ch; margin-bottom: 4px; }
.part-count { font: 500 .85rem/1 var(--font-ui); color: var(--muted); }
.chapter-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(320px, 1fr)); gap: 18px; }
.chapter-card { border: var(--border-w) solid var(--border); border-radius: var(--radius); padding: 20px; background: var(--surface); display: flex; flex-direction: column; }
.chapter-title { font-size: 1.1rem; margin-bottom: 8px; }
.chapter-num { font-family: var(--font-num); color: var(--accent-strong); margin-right: 4px; }
.chapter-intro { font-size: .9rem; color: var(--muted); }
.section-list { list-style: none; padding: 0; margin: 4px 0 auto; font: 400 .92rem/1.35 var(--font-ui); }
.section-list a { display: flex; gap: 10px; padding: 7px 0; border-top: var(--border-w) solid var(--border); text-decoration: none; color: var(--text); align-items: baseline; }
.section-list a:hover .t { color: var(--accent-strong); }
.section-list .num { font-family: var(--font-num); color: var(--muted); font-size: .82rem; min-width: 2.6em; }
.section-list .t { flex: 1; }
.section-list .count { font: 500 .78rem/1 var(--font-num); color: var(--muted); }

/* ---- problem bank ----------------------------------------------------------------------- */
.bank-layout { padding-bottom: 64px; }
.filters { display: flex; flex-wrap: wrap; gap: 12px 16px; align-items: center; padding: 14px; border: var(--border-w) solid var(--border); border-radius: var(--radius); background: var(--surface); margin-bottom: 14px; }
.filter-search { flex: 1 1 260px; }
.filters input[type="search"], .filters select { width: 100%; font: 400 .95rem/1.2 var(--font-ui); color: var(--text); background: var(--bg); border: var(--border-w) solid var(--border-strong); border-radius: var(--btn-radius); padding: 9px 12px; }
.filters select { width: auto; }
.filter-group { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; }
.chips { border: 0; padding: 0; margin: 0; display: flex; gap: 6px; flex-wrap: wrap; }
.chip { position: relative; }
.chip input { position: absolute; opacity: 0; inset: 0; cursor: pointer; }
.chip span { display: inline-block; font: 500 .85rem/1 var(--font-ui); padding: 8px 12px; border-radius: 999px; border: var(--border-w) solid var(--border-strong); color: var(--muted); background: var(--bg); }
.chip input:checked + span { background: var(--accent-soft); border-color: var(--accent); color: var(--text); }
.chip input:focus-visible + span { outline: 2px solid var(--focus); outline-offset: 2px; }
.result-count { font: 500 .85rem/1 var(--font-ui); color: var(--muted); margin: 18px 0 10px; }
.table-card { border: var(--border-w) solid var(--border); border-radius: var(--radius); overflow: hidden; background: var(--surface); }
.bank-table { width: 100%; border-collapse: collapse; font-family: var(--font-ui); font-size: .93rem; }
.bank-table th { text-align: left; font: 600 .85rem/1 var(--font-ui); color: var(--muted); padding: 12px 14px; border-bottom: var(--border-w) solid var(--border); background: var(--surface-2); }
.bank-table td { padding: 12px 14px; border-bottom: var(--border-w) solid var(--border); vertical-align: middle; }
.bank-table tbody tr:last-child td { border-bottom: 0; }
.bank-table tbody tr:hover { background: var(--surface-2); }
.bank-table .c-status { width: 36px; padding-right: 0; }
.bank-table .c-num { width: 64px; font-family: var(--font-num); color: var(--muted); font-size: .85rem; }
.bank-table .c-title a { color: var(--text); font-weight: 600; text-decoration: none; }
.bank-table .c-title a:hover { color: var(--accent-strong); text-decoration: underline; }
.bank-table .c-sub { display: block; font-size: .8rem; color: var(--muted); margin-top: 3px; }
.bank-table .c-topic { color: var(--muted); font-size: .88rem; }
.bank-table .c-diff { width: 120px; }
.bank-table .c-access { width: 80px; text-align: right; }
.bank-table .empty { text-align: center; color: var(--muted); padding: 40px; }

/* ---- home ------------------------------------------------------------------------------- */
.hero { padding: 64px 0 56px; border-bottom: var(--border-w) solid var(--border); }
.hero-inner { display: grid; grid-template-columns: minmax(0, 1.15fr) minmax(0, 1fr); gap: 56px; align-items: center; }
.hero-title { font-size: clamp(2.1rem, 1.4rem + 2.6vw, 3.4rem); line-height: 1.08; margin-bottom: 18px; }
.hero-title .hl { color: var(--accent-strong); }
.hero-cta { display: flex; gap: 12px; flex-wrap: wrap; margin: 26px 0 30px; }
.hero-stats { list-style: none; display: flex; gap: 34px; padding: 0; margin: 0; font-family: var(--font-ui); }
.hero-stats strong { display: block; font: 700 1.7rem/1.1 var(--font-num); }
.hero-stats span { color: var(--muted); font-size: .88rem; }
.hero-card { display: block; text-decoration: none; color: var(--text); background: var(--surface); border: var(--border-w) solid var(--border); border-radius: var(--radius-lg); padding: 24px 26px; box-shadow: var(--shadow-lg); }
.hero-card:hover { border-color: var(--accent); color: var(--text); }
.hero-card-title { font: 700 1.25rem/1.25 var(--font-heading); margin: 6px 0 12px; }
.hero-card-body { font-size: .95rem; color: var(--text); }
.hero-card-cta { font: 600 .92rem/1 var(--font-ui); color: var(--accent-strong); }
.features { padding: 56px 0; }
.feature-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 28px; }
.feature h2 { font-size: 1.1rem; margin: 12px 0 8px; }
.feature p { color: var(--muted); font-size: .95rem; }
.feature-icon { display: inline-grid; place-items: center; width: 34px; height: 34px; border-radius: var(--radius-sm); background: var(--accent-soft); color: var(--accent-strong); font: 700 .95rem/1 var(--font-num); }
.topics { padding: 8px 0 56px; }
.section-heading { font-size: 1.5rem; margin-bottom: 18px; }
.topic-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 14px; }
.topic { display: flex; flex-direction: column; gap: 6px; padding: 18px; border: var(--border-w) solid var(--border); border-radius: var(--radius); text-decoration: none; color: var(--text); background: var(--surface); }
.topic:hover { border-color: var(--accent); color: var(--text); }
.topic-num { font: 700 .82rem/1 var(--font-num); color: var(--accent-strong); }
.topic-title { font: 650 1rem/1.25 var(--font-heading); }
.topic-count { font-size: .82rem; color: var(--muted); font-family: var(--font-ui); }
.cta-band { background: var(--bg-2); border-top: var(--border-w) solid var(--border); padding: 44px 0; }
.cta-inner { display: flex; justify-content: space-between; align-items: center; gap: 24px; flex-wrap: wrap; }
.cta-inner h2 { font-size: 1.45rem; margin-bottom: 6px; }
.cta-inner p { color: var(--muted); margin: 0; }

/* ---- pricing ---------------------------------------------------------------------------- */
.pricing-layout { padding-bottom: 64px; }
.placeholder-note { font: 500 .8rem/1 var(--font-ui); color: var(--muted); margin-top: 10px; }
.plans { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; align-items: stretch; margin: 10px 0 56px; }
.plan { border: var(--border-w) solid var(--border); border-radius: var(--radius-lg); padding: 26px; background: var(--surface); display: flex; flex-direction: column; position: relative; }
.plan-featured { border: 2px solid var(--accent); box-shadow: var(--shadow-lg); }
.plan-flag { position: absolute; top: -12px; left: 26px; background: var(--accent); color: var(--on-accent); font: 600 .82rem/1 var(--font-ui); padding: 6px 10px; border-radius: 999px; margin: 0; }
.plan-name { font-size: 1.15rem; margin-bottom: 10px; }
.plan-price { margin: 0 0 10px; font-family: var(--font-num); }
.plan-price .amount { font-size: 2.5rem; font-weight: 700; letter-spacing: -0.02em; }
.plan-price .per { color: var(--muted); margin-left: 6px; font-family: var(--font-ui); }
.plan-blurb { color: var(--muted); font-size: .93rem; min-height: 3em; }
.plan-features { list-style: none; padding: 0; margin: 6px 0 24px; flex: 1; font-size: .93rem; }
.plan-features li { padding: 7px 0 7px 24px; position: relative; border-top: var(--border-w) solid var(--border); }
.plan-features li::before { content: "✓"; position: absolute; left: 0; color: var(--good); font-weight: 700; }
.faq { max-width: 760px; }
.faq details { border-top: var(--border-w) solid var(--border); padding: 14px 0; }
.faq summary { cursor: pointer; font: 600 1rem/1.3 var(--font-ui); }
.faq details p { color: var(--muted); margin: 10px 0 0; }

/* ---- footer, review page ---------------------------------------------------------------- */
.site-footer { border-top: var(--border-w) solid var(--border); padding: 30px 0 70px; font-family: var(--font-ui); font-size: .88rem; color: var(--muted); background: var(--bg); }
.footer-inner { display: flex; justify-content: space-between; gap: 24px; flex-wrap: wrap; }
.footer-brand .brand-name { font: 700 1rem/1 var(--font-heading); color: var(--text); }
.footer-brand p { margin: 6px 0 0; }
.footer-nav { display: flex; gap: 18px; flex-wrap: wrap; }
.footer-nav a { color: var(--muted); text-decoration: none; }
.footer-nav a:hover { color: var(--text); }
.review { padding-bottom: 80px; }
.review-block { border-top: var(--border-w) solid var(--border); padding: 30px 0; }
.review-block h2 { font-size: 1.5rem; margin-bottom: 6px; }
.review-block > p { color: var(--muted); max-width: 80ch; }
.dev-mail { white-space: pre-wrap; font: 400 .9rem/1.5 var(--font-mono); background: var(--surface); border: var(--border-w) solid var(--border); border-radius: var(--radius); padding: 14px; }
.findings-table td { font-size: .88rem; vertical-align: top; }
.findings-table .c-sub-cell { color: var(--muted); }

/* ---- answer checking, locked problems, reports ------------------------------------------- */
.answer-part { display: inline-flex; align-items: center; gap: 8px; flex: 1 1 180px; min-width: 0; }
.answer-part .answer-input { flex: 1 1 auto; }
.part-label { font: 600 .85rem/1.2 var(--font-ui); color: var(--muted); white-space: nowrap; }
.answer-input:disabled { opacity: .6; }
.answer-feedback.ok { color: var(--good); }
.answer-feedback.no { color: var(--bad); }
.answer-feedback.note { color: var(--muted); }
.answer-input.is-correct { border-color: var(--good); }
.answer-input.is-wrong { border-color: var(--bad); }
.solution-body .loading { color: var(--muted); font-family: var(--font-ui); font-size: .9rem; }
.variation-head { display: flex; align-items: center; gap: 10px; }
.bookmark { margin-left: auto; font-size: .88rem; }
.bookmark.on { font-weight: 600; text-decoration: none; }
.locked-panel { border: var(--border-w) solid var(--border-strong); border-radius: var(--radius); background: var(--surface); padding: 26px 28px; margin: 26px 0; max-width: var(--measure); font-family: var(--font-ui); }
.locked-panel h2 { font-size: 1.3rem; margin-bottom: 8px; }
.locked-panel p { color: var(--muted); }
.locked-actions { display: flex; gap: 10px; flex-wrap: wrap; margin: 14px 0 10px; }
.locked-free { font-size: .92rem; margin: 10px 0 0; }
details.report > summary { list-style: none; cursor: pointer; display: inline; color: var(--muted); font-size: .85rem; }
details.report > summary::-webkit-details-marker { display: none; }
.report-form { margin-top: 12px; max-width: var(--measure); display: grid; gap: 8px; font-family: var(--font-ui); }
.report-form label { font: 500 .88rem/1.4 var(--font-ui); color: var(--text); }
.report-form textarea, .report-form select { font: 400 .95rem/1.4 var(--font-ui); color: var(--text); background: var(--bg); border: var(--border-w) solid var(--border-strong); border-radius: var(--btn-radius); padding: 9px 11px; }
.report-form .btn { justify-self: start; }
.report-feedback { margin: 0; font-size: .9rem; color: var(--good); }
.aside-list a .status { margin-top: 2px; }

/* ---- messages, account and sign-in pages ------------------------------------------------- */
.messages { list-style: none; padding: 0; margin: 18px 0 0; }
.message { padding: 12px 16px; border-radius: var(--radius); background: var(--accent-soft); color: var(--text); font: 500 .92rem/1.4 var(--font-ui); margin-bottom: 8px; }
.message.error { background: var(--bad-soft); color: var(--bad); }
.message.success { background: var(--good-soft); color: var(--good); }
.auth-layout { display: flex; justify-content: center; padding: 48px 24px 72px; }
.auth-card { width: 100%; max-width: 440px; background: var(--surface); border: var(--border-w) solid var(--border); border-radius: var(--radius-lg); padding: 30px 32px; font-family: var(--font-ui); }
.auth-card h1 { font-size: 1.6rem; margin-bottom: 14px; }
.auth-card h2 { font-size: 1.15rem; margin: 18px 0 10px; }
.auth-card p { color: var(--muted); font-size: .95rem; }
.auth-card form { margin: 18px 0 8px; }
.auth-card label { display: block; font: 600 .88rem/1.3 var(--font-ui); margin-bottom: 6px; color: var(--text); }
.auth-card input[type="email"], .auth-card input[type="password"], .auth-card input[type="text"] { width: 100%; font: 400 1rem/1.2 var(--font-ui); color: var(--text); background: var(--bg); border: var(--border-w) solid var(--border-strong); border-radius: var(--btn-radius); padding: 11px 13px; margin-bottom: 4px; }
.auth-card input:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.auth-card input[type="checkbox"] { margin-right: 8px; }
.auth-card input[type="checkbox"] + label, .auth-card label:has(input[type="checkbox"]) { display: inline; font-weight: 400; }
.auth-card button, .auth-card .button { display: inline-flex; justify-content: center; width: 100%; margin-top: 14px; font: 600 .95rem/1 var(--font-ui); padding: 12px 18px; border-radius: var(--btn-radius); border: 0; background: var(--accent); color: var(--on-accent); cursor: pointer; }
.auth-card button:hover { background: var(--accent-strong); }
.auth-card button[type="submit"][name="action_remove"], .auth-card button[name="action_send"] { background: var(--surface); color: var(--text); border: var(--border-w) solid var(--border-strong); }
.auth-card .errorlist { list-style: none; padding: 0; margin: 4px 0 8px; color: var(--bad); font-size: .88rem; }
.auth-card ul { padding-left: 1.2em; color: var(--muted); font-size: .9rem; }
.auth-card .helptext, .auth-card .help-text { display: block; color: var(--muted); font-size: .82rem; margin-top: 4px; }
.auth-card p:has(> input) { margin: 0 0 12px; }
.account-layout { padding-bottom: 72px; }
.account-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 18px; margin-top: 8px; }
.account-card { border: var(--border-w) solid var(--border); border-radius: var(--radius); background: var(--surface); padding: 20px 22px; font-family: var(--font-ui); }
.account-card h2 { font-size: 1.15rem; margin-bottom: 10px; }
.account-card p { color: var(--muted); font-size: .93rem; }
.account-card form { display: inline; }
.account-card .btn { margin: 6px 8px 0 0; }
.stat-big { font: 700 1.9rem/1.1 var(--font-num); color: var(--text); }
.bookmark-list { list-style: none; padding: 0; margin: 6px 0 0; }
.bookmark-list li { padding: 7px 0; border-top: var(--border-w) solid var(--border); font-size: .93rem; }
.bookmark-list .num { color: var(--muted); font-size: .82rem; margin-right: 8px; }

/* ---- responsive ------------------------------------------------------------------------- */
@media (max-width: 1040px) {
  .problem-layout, .section-layout { grid-template-columns: minmax(0, 1fr); gap: 0; }
  .problem-aside, .section-aside { position: static; padding-top: 0; margin-bottom: 48px; }
  .hero-inner { grid-template-columns: 1fr; gap: 36px; }
  .topic-grid { grid-template-columns: repeat(2, 1fr); }
  .plans { grid-template-columns: 1fr; max-width: 520px; margin-left: auto; margin-right: auto; }
}
@media (max-width: 720px) {
  :root { --fs-body: 16.5px; }
  .wrap { padding: 0 18px; }
  .header-inner { height: auto; flex-wrap: wrap; gap: 6px 16px; padding-top: 10px; padding-bottom: 8px; }
  .site-nav { order: 3; width: 100%; gap: 18px; overflow-x: auto; }
  .header-actions .btn-ghost { display: none; }
  .feature-grid { grid-template-columns: 1fr; }
  .problem-row a { grid-template-columns: 16px 3em minmax(0, 1fr) auto; }
  .problem-row .difficulty .d-label { display: none; }
  .problem-row .badge { display: none; }
  .bank-table .c-topic, .bank-table .c-status { display: none; }
  .bank-table .difficulty .d-label { display: none; }
  .bank-table .c-diff { width: auto; }
  .hero-stats { gap: 22px; }
}