/* Всезнайка — mobile-first, темы через data-theme, ~14KB до сжатия */
:root {
  --bg: #f7f8fb;
  --card: #ffffff;
  --ink: #171923;
  --mut: #6b7280;
  --line: #e6e8f0;
  --ac1: #6366f1;
  --ac2: #06b6d4;
  --ac1-soft: #eef0fe;
  --ok: #10b981;
  --shadow: 0 1px 2px rgb(20 24 40 / .05), 0 8px 24px -12px rgb(20 24 40 / .12);
  --r: 16px;
  color-scheme: light;
}
:root[data-theme="dark"] {
  --bg: #0e1015;
  --card: #171a22;
  --ink: #eceef4;
  --mut: #98a0b3;
  --line: #262b38;
  --ac1: #818cf8;
  --ac2: #22d3ee;
  --ac1-soft: #22263c;
  --ok: #34d399;
  --shadow: 0 1px 2px rgb(0 0 0 / .4), 0 8px 24px -12px rgb(0 0 0 / .5);
  color-scheme: dark;
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font: 400 16px/1.6 Manrope, system-ui, -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--ink);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeSpeed;
}
img, svg { max-width: 100%; }
a { color: var(--ac1); text-decoration: none; }
h1 { font-size: clamp(1.55rem, 4.5vw, 2.25rem); line-height: 1.2; font-weight: 800; margin: .6em 0 .4em; letter-spacing: -.02em; }
h2 { font-size: clamp(1.2rem, 3vw, 1.5rem); font-weight: 800; margin: 1.4em 0 .6em; letter-spacing: -.01em; }
.lead { color: var(--mut); max-width: 62ch; margin-bottom: 1rem; }
.wrap { max-width: 1080px; margin: 0 auto; padding: 0 16px; }
.wrap--narrow { max-width: 760px; }
.i { width: 1.15em; height: 1.15em; vertical-align: -.22em; flex: none; }
.skip { position: absolute; left: -9999px; }
.skip:focus { left: 8px; top: 8px; z-index: 99; background: var(--card); padding: 8px 14px; border-radius: 8px; }

/* ── Шапка ─────────────────────────────────────────── */
.hdr { position: sticky; top: 0; z-index: 50; background: color-mix(in srgb, var(--card) 85%, transparent); backdrop-filter: blur(12px); border-bottom: 1px solid var(--line); }
.hdr__in { display: flex; align-items: center; gap: 12px; height: 60px; }
.logo { display: flex; align-items: center; gap: 8px; font-size: 1.2rem; font-weight: 800; color: var(--ink); letter-spacing: -.02em; }
.logo em { font-style: normal; color: var(--ac1); }
.logo-mark { width: 30px; height: 30px; flex: none; }
.hdr__nav { display: none; gap: 4px; }
.hdr__nav a { color: var(--ink); font-weight: 700; font-size: .95rem; padding: 8px 12px; border-radius: 10px; }
.hdr__nav a:hover { background: var(--ac1-soft); color: var(--ac1); }

.srch { display: none; flex: 1; max-width: 420px; position: relative; }
.srch input { width: 100%; height: 42px; border: 1.5px solid var(--line); border-radius: 12px; background: var(--bg); color: var(--ink); padding: 0 46px 0 14px; font: inherit; font-size: .95rem; transition: border-color .15s; }
.srch input:focus { outline: none; border-color: var(--ac1); }
.srch button { position: absolute; right: 4px; top: 4px; bottom: 4px; border: 0; background: none; color: var(--mut); padding: 0 10px; cursor: pointer; border-radius: 9px; display: flex; align-items: center; gap: 6px; }
.srch button:hover { color: var(--ac1); }
.srch--hero { display: flex; max-width: 560px; margin: 1.2rem 0; }
.srch--hero input { height: 52px; border-radius: 14px; background: var(--card); box-shadow: var(--shadow); padding-right: 116px; }
.srch--hero button { background: linear-gradient(135deg, var(--ac1), var(--ac2)); color: #fff; font-weight: 700; padding: 0 18px; }
.srch--hero button:hover { color: #fff; filter: brightness(1.08); }

.tgl, .burger { border: 1.5px solid var(--line); background: var(--card); color: var(--ink); width: 40px; height: 40px; border-radius: 12px; cursor: pointer; display: grid; place-items: center; flex: none; }
.tgl:hover, .burger:hover { border-color: var(--ac1); color: var(--ac1); }
.tgl { margin-left: auto; }
.tgl__moon { display: none; }
:root[data-theme="dark"] .tgl__sun { display: none; }
:root[data-theme="dark"] .tgl__moon { display: block; }
.mnav { display: grid; gap: 2px; padding: 8px 16px 14px; border-top: 1px solid var(--line); background: var(--card); }
.mnav[hidden] { display: none; }
.mnav a { display: flex; align-items: center; gap: 10px; padding: 12px; border-radius: 12px; color: var(--ink); font-weight: 700; }
.mnav a:hover { background: var(--ac1-soft); }

/* ── Герой ─────────────────────────────────────────── */
.hero { background: linear-gradient(160deg, var(--ac1-soft), transparent 60%); border-bottom: 1px solid var(--line); }
.hero__in { display: grid; gap: 8px; padding: 34px 16px 30px; }
.hero h1 { font-size: clamp(2rem, 7vw, 3.1rem); margin: 0 0 .35em; }
.hero h1 em { font-style: normal; background: linear-gradient(90deg, var(--ac1), var(--ac2)); -webkit-background-clip: text; background-clip: text; color: transparent; }
.hero p { color: var(--mut); max-width: 52ch; }
.hero__badges { display: flex; flex-wrap: wrap; gap: 8px 18px; font-size: .88rem; font-weight: 700; color: var(--mut); }
.hero__badges .i { color: var(--ac1); }
.hero__art { display: none; }

/* ── Сетки ─────────────────────────────────────────── */
.sec { margin: 26px auto; }
.sec__head { display: flex; align-items: baseline; justify-content: space-between; gap: 12px; }
.more { font-weight: 700; font-size: .92rem; white-space: nowrap; }
.grades { display: grid; grid-template-columns: repeat(auto-fill, minmax(76px, 1fr)); gap: 10px; }
.grade { display: grid; place-items: center; gap: 0; background: var(--card); border: 1.5px solid var(--line); border-radius: var(--r); padding: 12px 6px; color: var(--ink); transition: transform .12s, border-color .12s; }
.grade b { font-size: 1.5rem; font-weight: 800; color: var(--ac1); line-height: 1.1; }
.grade span { font-size: .78rem; color: var(--mut); }
.grade:hover { transform: translateY(-2px); border-color: var(--ac1); }
.subjects { display: grid; grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); gap: 10px; }
.subject { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; background: var(--card); border: 1.5px solid var(--line); border-radius: var(--r); padding: 13px 14px; color: var(--ink); font-weight: 700; font-size: .95rem; transition: transform .12s, border-color .12s; }
.subject .i { width: 1.35em; height: 1.35em; color: var(--c, var(--ac1)); }
.subject small { flex-basis: 100%; color: var(--mut); font-weight: 500; }
.subject:hover { transform: translateY(-2px); border-color: var(--c, var(--ac1)); }

.grid-cards { display: grid; grid-template-columns: 1fr; gap: 12px; }
.card { background: var(--card); border: 1.5px solid var(--line); border-radius: var(--r); padding: 16px; color: var(--ink); display: flex; flex-direction: column; gap: 8px; transition: transform .12s, border-color .12s, box-shadow .12s; }
.card:hover { transform: translateY(-2px); border-color: var(--ac1); box-shadow: var(--shadow); }

.book-card { flex-direction: row; align-items: center; gap: 14px; }
.book-card__cover { position: relative; display: grid; place-items: center; width: 56px; height: 72px; flex: none; border-radius: 10px; background: color-mix(in srgb, var(--c, var(--ac1)) 14%, var(--card)); color: var(--c, var(--ac1)); border: 1.5px solid color-mix(in srgb, var(--c, var(--ac1)) 35%, var(--line)); }
.book-card__cover .i { width: 1.6em; height: 1.6em; }
.book-card__cover b { position: absolute; right: 5px; bottom: 3px; font-size: .72rem; }
.book-card__cover--lg { width: 74px; height: 96px; }
.book-card__title { font-weight: 800; line-height: 1.35; }
.book-card__meta, .q-card__meta, .art-card__meta { font-size: .85rem; color: var(--mut); display: flex; align-items: center; gap: 6px; flex-wrap: wrap; }
.dot { width: 3px; height: 3px; border-radius: 50%; background: var(--mut); }
.q-card__title, .art-card__title { font-weight: 800; line-height: 1.4; }
.art-card__ex { font-size: .9rem; color: var(--mut); }
.chip { align-self: flex-start; display: inline-block; font-size: .78rem; font-weight: 800; color: var(--c, var(--ac1)); background: color-mix(in srgb, var(--c, var(--ac1)) 12%, transparent); padding: 3px 10px; border-radius: 99px; }

/* ── Хлебные крошки / номера ───────────────────────── */
.bc { margin: 14px 0 4px; font-size: .85rem; }
.bc ol { display: flex; flex-wrap: wrap; gap: 6px; list-style: none; color: var(--mut); }
.bc a { color: var(--mut); }
.bc a:hover { color: var(--ac1); }
.bc-sep { opacity: .5; }
.nums { display: grid; grid-template-columns: repeat(auto-fill, minmax(58px, 1fr)); gap: 8px; margin: 10px 0 20px; }
.nums a { display: grid; place-items: center; height: 44px; background: var(--card); border: 1.5px solid var(--line); border-radius: 10px; font-weight: 800; font-size: .92rem; color: var(--ink); }
.nums a:hover { border-color: var(--ac1); color: var(--ac1); }

/* ── Панели условия/решения ────────────────────────── */
.book-head { display: flex; gap: 16px; align-items: flex-start; margin-top: 10px; }
.book-head h1 { margin-top: 0; }
.book-head__meta, .task-src, .q-stats { color: var(--mut); font-size: .9rem; margin-bottom: 8px; }
.panel { background: var(--card); border: 1.5px solid var(--line); border-radius: var(--r); margin: 14px 0; overflow: hidden; }
.panel__label { display: flex; align-items: center; gap: 8px; font-size: .85rem; font-weight: 800; text-transform: uppercase; letter-spacing: .06em; color: var(--mut); padding: 12px 18px 0; margin: 0; }
.panel__body { padding: 12px 18px 18px; overflow-x: auto; }
.panel--q { border-left: 4px solid var(--ac2); }
.panel--s { border-left: 4px solid var(--ac1); }
.panel--verified { border-left: 4px solid var(--ok); }
.panel--a .panel__body { padding-top: 4px; }
.panel__ahead { display: flex; align-items: center; gap: 10px; padding: 14px 18px 6px; }
.avatar { display: grid; place-items: center; width: 34px; height: 34px; border-radius: 50%; background: linear-gradient(135deg, var(--ac1), var(--ac2)); color: #fff; font-weight: 800; font-size: .95rem; }
.badge { display: inline-flex; align-items: center; gap: 4px; font-size: .78rem; font-weight: 800; color: var(--ok); background: color-mix(in srgb, var(--ok) 12%, transparent); padding: 3px 10px; border-radius: 99px; }
.rating { margin-left: auto; color: var(--mut); font-weight: 700; font-size: .88rem; display: flex; align-items: center; gap: 4px; }
.solution p { margin: .6em 0; }
.solution ol, .solution ul, .article__body ol, .article__body ul { padding-left: 1.3em; margin: .6em 0; }
.solution li { margin: .35em 0; }
.solution .formula { display: block; overflow-x: auto; background: var(--bg); border-radius: 10px; padding: 10px 14px; margin: .6em 0; font-family: ui-monospace, "Cascadia Mono", monospace; font-size: .95rem; }
.solution .note { color: var(--mut); font-size: .92rem; border-left: 3px solid var(--ac2); padding-left: 12px; margin: .8em 0; }
.answer { border-top: 1.5px dashed var(--line); padding: 12px 18px; background: color-mix(in srgb, var(--ok) 6%, transparent); }
.answer b { color: var(--ok); }

.pager { display: flex; align-items: center; justify-content: space-between; gap: 10px; margin: 20px 0; }
.pager__a, .pager__all { display: inline-flex; align-items: center; gap: 6px; font-weight: 800; background: var(--card); border: 1.5px solid var(--line); padding: 10px 16px; border-radius: 12px; color: var(--ink); }
.pager__a:hover, .pager__all:hover { border-color: var(--ac1); color: var(--ac1); }
.pager--pages { justify-content: center; flex-wrap: wrap; }
.pg { display: grid; place-items: center; min-width: 40px; height: 40px; border-radius: 10px; border: 1.5px solid var(--line); background: var(--card); color: var(--ink); font-weight: 800; }
.pg--cur { background: var(--ac1); border-color: var(--ac1); color: #fff; }

/* ── Статьи ────────────────────────────────────────── */
.article__body { max-width: 68ch; }
.article__body p { margin: .8em 0; }
.article__body h2 { margin-top: 1.6em; }
.article__body blockquote { border-left: 3px solid var(--ac1); padding: 4px 0 4px 16px; color: var(--mut); margin: 1em 0; }

/* ── Реклама (фиксированные высоты → CLS 0) ────────── */
.ad { position: relative; display: grid; place-items: center; background: repeating-linear-gradient(45deg, var(--bg), var(--bg) 12px, color-mix(in srgb, var(--line) 40%, var(--bg)) 12px, color-mix(in srgb, var(--line) 40%, var(--bg)) 24px); border: 1.5px dashed var(--line); border-radius: var(--r); margin: 16px 0; }
.ad__hint { font-size: .78rem; color: var(--mut); background: var(--card); padding: 3px 10px; border-radius: 99px; border: 1px solid var(--line); }
.ad--sidebar { position: sticky; top: 76px; }
.ad-sticky { position: fixed; left: 0; right: 0; bottom: 0; z-index: 60; height: 62px; display: grid; place-items: center; background: var(--card); border-top: 1.5px solid var(--line); box-shadow: 0 -6px 20px rgb(0 0 0 / .08); }
.ad-sticky__close { position: absolute; right: 6px; top: 6px; border: 0; background: var(--bg); color: var(--mut); width: 26px; height: 26px; border-radius: 50%; cursor: pointer; display: grid; place-items: center; }
.ad-sticky[hidden] { display: none; }
body:has(.ad-sticky:not([hidden])) { padding-bottom: 66px; }

/* ── Пусто / 404 / футер ───────────────────────────── */
.empty { text-align: center; color: var(--mut); padding: 40px 16px; }
.empty .i { width: 42px; height: 42px; opacity: .5; }
.empty--404 { padding: 60px 16px; }
.e404 { width: 240px; margin: 0 auto; }
.ftr { border-top: 1px solid var(--line); background: var(--card); margin-top: 40px; }
.ftr__in { display: grid; gap: 24px; padding: 30px 16px 10px; }
.ftr__brand { display: grid; grid-template-columns: 30px 1fr; gap: 8px 10px; align-items: center; font-weight: 800; font-size: 1.1rem; }
.ftr__brand em { font-style: normal; color: var(--ac1); }
.ftr__brand p { grid-column: 1 / -1; font-weight: 500; font-size: .9rem; color: var(--mut); }
.ftr__col { display: grid; gap: 8px; align-content: start; font-size: .95rem; }
.ftr__col b { margin-bottom: 2px; }
.ftr__col a { color: var(--mut); }
.ftr__col a:hover { color: var(--ac1); }
.ftr__copy { padding: 14px 16px 22px; color: var(--mut); font-size: .85rem; }

/* ── Планшет и десктоп ─────────────────────────────── */
@media (min-width: 640px) {
  .grid-cards { grid-template-columns: repeat(2, 1fr); }
  .hero__in { grid-template-columns: 1.2fr .8fr; align-items: center; padding: 48px 16px; }
  .hero__art { display: block; }
}
@media (min-width: 900px) {
  .srch { display: flex; }
  .hdr__nav { display: flex; }
  .burger, .mnav { display: none !important; }
  .grid-cards { grid-template-columns: repeat(3, 1fr); }
  .grid-cards--q { grid-template-columns: repeat(2, 1fr); }
  .wrap--cols { display: grid; grid-template-columns: minmax(0, 1fr) 300px; gap: 28px; align-items: start; }
  .ad-sticky { display: none; }
  body:has(.ad-sticky) { padding-bottom: 0; }
}
@media (max-width: 899px) { .col-side { display: none; } }
/* Реклама выключена → пустой сайдбар схлопывается, контент занимает всю ширину */
.col-side:empty { display: none; }
@media (min-width: 900px) { .wrap--cols:has(.col-side:empty) { grid-template-columns: minmax(0, 1fr); } }
@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; animation: none !important; }
  html { scroll-behavior: auto; }
}