/* Оболочка «Тетрадь»: лист в клетку, синяя ручка и красная пометка, школьная доска — акцентами.
   Тёмная тема — «ночная тетрадь»: тёмно-синий лист в клетку и меловые надписи. */
body.bz-skin-tetrad {
  --bz-bg: #FCFBF7; --bz-panel: #FFFFFF; --bz-soft: #F1F4F9; --bz-line: #D5DCE6;
  --bz-ink: #1C2433; --bz-text: #2B3446; --bz-mute: #56617A;
  --bz-acc: #1F4FB8; --bz-on-acc: #FFFFFF; --bz-acc-soft: #EAF0FB; --bz-acc-ink: #1F4FB8;
  --bz-red: #D9534F; --bz-red-ink: #B3261E;
  --bz-ok: #1C7A46; --bz-ok-bg: #E8F6EE; --bz-ok-ink: #17663A;
  --bz-warn: #C97A00; --bz-warn-bg: #FFF4DA; --bz-warn-ink: #7A4A00;
  --bz-bad: #C62D2A; --bz-bad-bg: #FDEDEC; --bz-bad-ink: #A8221F;
  --bz-none: #EEF1F6; --bz-none-ink: #56617A;
  --bz-radius: 6px; --bz-radius-sm: 4px;
  --bz-font: "Golos Text", system-ui, sans-serif;
  --bz-font-d: "Golos Text", system-ui, sans-serif;
  --bz-hand: Caveat, "Segoe Print", cursive;
  --bz-chalk: Neucha, Caveat, cursive;
  --bz-grid: #E1E8F2; --bz-grid-size: 22px;
  --bz-board: #24433A; --bz-board-ink: #F3F1E8; --bz-board-mute: rgba(243,241,232,.78); --bz-board-acc: #F5D76E;
  --bz-wood: #8A5A35; --bz-sticky: #FFF9C9; --bz-sticky-2: #E3F0FF;
  --bz-shadow: 0 2px 0 var(--bz-line);
  --bz-max: 1240px;
}
html[data-theme="dark"] body.bz-skin-tetrad {
  --bz-bg: #141B2B; --bz-panel: #1B2436; --bz-soft: #222D42; --bz-line: #33415C;
  --bz-ink: #EEF2FA; --bz-text: #D7DEEC; --bz-mute: #A3AEC4;
  --bz-acc: #8FB2FF; --bz-on-acc: #0E1626; --bz-acc-soft: #23345A; --bz-acc-ink: #A9C3FF;
  --bz-red: #FF8A84; --bz-red-ink: #FFA29D;
  --bz-ok: #7FDCA6; --bz-ok-bg: #173527; --bz-ok-ink: #9BE8BA;
  --bz-warn: #FFC260; --bz-warn-bg: #3A2E16; --bz-warn-ink: #FFD08A;
  --bz-bad: #FF8F8B; --bz-bad-bg: #3D2023; --bz-bad-ink: #FFAAA6;
  --bz-none: #222D42; --bz-none-ink: #A3AEC4;
  --bz-grid: rgba(143,178,255,.09);
  --bz-board: #1E3B33; --bz-wood: #6E4628; --bz-sticky: #3B3820; --bz-sticky-2: #20304D;
  --bz-shadow: 0 2px 0 rgba(0,0,0,.35);
  color-scheme: dark;
}

/* лист в клетку */
body.bz-skin-tetrad {
  background-color: var(--bz-bg);
  background-image: linear-gradient(var(--bz-grid) 1px, transparent 1px), linear-gradient(90deg, var(--bz-grid) 1px, transparent 1px);
  background-size: var(--bz-grid-size) var(--bz-grid-size);
}
.bz-skin-tetrad .bz-hand { font-family: var(--bz-hand); font-weight: 700; }
.bz-skin-tetrad .bz-red { color: var(--bz-red); }

/* ---------- Шапка ---------- */
.bz-skin-tetrad .bz-top { background: var(--bz-panel); border-bottom: 2px solid var(--bz-acc); }
.bz-skin-tetrad .bz-top-in { min-height: 70px; }
.bz-skin-tetrad .bz-brand { font-family: var(--bz-hand); font-size: 34px; font-weight: 700; color: var(--bz-acc) !important; letter-spacing: 0; }
.bz-skin-tetrad .bz-brand-dot { color: var(--bz-red); }
.bz-skin-tetrad .bz-nav-a { border-radius: 0; color: var(--bz-ink) !important; font-weight: 500; padding: 0 10px; background: transparent !important; }
.bz-skin-tetrad .bz-nav-a::after { content: ""; position: absolute; left: 10px; right: 10px; bottom: 8px; height: 2px; background: var(--bz-red); transform: scaleX(0); transform-origin: left; transition: transform .25s ease; }
.bz-skin-tetrad .bz-nav-a:hover::after, .bz-skin-tetrad .bz-nav-a.is-on::after { transform: scaleX(1); }
.bz-skin-tetrad .bz-nav-a.is-on { color: var(--bz-acc-ink) !important; }
.bz-skin-tetrad .bz-nav-a .bz-ic { display: none; }
.bz-skin-tetrad .bz-nav-cta { background: var(--bz-red) !important; color: #FFFFFF !important; font-weight: 700; padding: 0 16px; margin-left: 4px; }
.bz-skin-tetrad .bz-nav-cta::after { display: none; }
.bz-skin-tetrad .bz-nav-cta:hover { filter: brightness(1.06); }
.bz-skin-tetrad .bz-theme-toggle { border-radius: var(--bz-radius-sm); border-style: dashed; }

/* ---------- Подвал ---------- */
.bz-skin-tetrad .bz-foot { border-top: 0; background: var(--bz-board); color: var(--bz-board-mute); margin-top: 24px; border-top: 10px solid var(--bz-wood); }
.bz-skin-tetrad .bz-foot a { color: var(--bz-board-ink); }
.bz-tfoot { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 24px; padding-top: 30px; padding-bottom: 26px; }
.bz-tfoot-brand { font-family: var(--bz-chalk); font-size: 30px; color: var(--bz-board-ink); text-decoration: none; }
.bz-tfoot h2 { font-family: var(--bz-chalk); font-weight: 400; font-size: 21px; color: var(--bz-board-ink); margin: 0 0 8px; }
.bz-tfoot ul { list-style: none; margin: 0; padding: 0; display: flex; flex-direction: column; gap: 6px; font-size: 15px; }
.bz-tfoot a { text-decoration: none; }
.bz-tfoot a:hover { text-decoration: underline; }
.bz-tfoot-copy { border-top: 1px dashed rgba(243,241,232,.3); padding-top: 14px; padding-bottom: 18px; font-size: 13px; display: flex; flex-wrap: wrap; gap: 8px 20px; justify-content: space-between; }

/* ---------- Заголовки ---------- */
.bz-skin-tetrad .bz-h1 { font-family: var(--bz-hand); font-weight: 700; font-size: clamp(36px, 5vw, 50px); line-height: 1; color: var(--bz-acc-ink); letter-spacing: 0; }
.bz-skin-tetrad .bz-h2 { font-family: var(--bz-hand); font-weight: 700; font-size: 34px; line-height: 1.05; color: var(--bz-acc-ink); }
.bz-skin-tetrad .bz-h3 { font-family: var(--bz-font); font-weight: 700; font-size: 18px; }
.bz-skin-tetrad .bz-eyebrow { font-family: var(--bz-hand); font-size: 24px; text-transform: none; letter-spacing: 0; color: var(--bz-red); }

/* ---------- Карточки и кнопки ---------- */
.bz-skin-tetrad .bz-card { border-radius: var(--bz-radius); box-shadow: var(--bz-shadow); }
.bz-skin-tetrad .bz-btn { border-radius: var(--bz-radius-sm); font-weight: 600; }
.bz-skin-tetrad .bz-btn-acc { background: var(--bz-acc); color: var(--bz-on-acc) !important; border-color: var(--bz-acc); }
.bz-skin-tetrad .bz-btn-ghost, .bz-skin-tetrad .bz-btn-line { border: 1px dashed var(--bz-mute); background: transparent; color: var(--bz-acc-ink) !important; }
.bz-skin-tetrad .bz-btn-red { background: var(--bz-red); border-color: var(--bz-red); color: #FFFFFF !important; }
.bz-skin-tetrad .bz-chip, .bz-skin-tetrad .bz-pill { border-radius: var(--bz-radius-sm); }
.bz-skin-tetrad .bz-seg { border-radius: var(--bz-radius-sm); }
.bz-skin-tetrad .bz-seg a, .bz-skin-tetrad .bz-seg button { border-radius: 2px; }

/* ---------- Задача ---------- */
.bz-skin-tetrad .bz-task { padding: 0; gap: 0; }
.bz-skin-tetrad .bz-task > * { padding-left: 22px; padding-right: 22px; }
.bz-skin-tetrad .bz-task-head { padding-top: 12px; padding-bottom: 12px; border-bottom: 1px dashed var(--bz-line); }
.bz-skin-tetrad .bz-task-title { font-family: var(--bz-hand); font-weight: 700; font-size: 30px; color: var(--bz-ink); }
.bz-skin-tetrad h2.bz-task-title { font-size: 28px; }
.bz-skin-tetrad .bz-cond { padding-top: 18px; }
.bz-skin-tetrad .bz-answer { padding-top: 6px; padding-bottom: 14px; }
.bz-skin-tetrad .bz-answer-l { font-family: var(--bz-hand); font-size: 26px; font-weight: 700; color: var(--bz-acc-ink); }
.bz-skin-tetrad .bz-answer input { border: 0; border-bottom: 2px solid var(--bz-ink); border-radius: 0; background: var(--bz-soft); }
.bz-skin-tetrad .bz-answer.is-ok input { border-bottom-color: var(--bz-ok); }
.bz-skin-tetrad .bz-answer.is-bad input { border-bottom-color: var(--bz-bad); }
.bz-skin-tetrad .bz-result { font-family: var(--bz-hand); font-size: 26px; font-weight: 700; }
.bz-skin-tetrad .bz-task-actions { padding-bottom: 16px; }
.bz-skin-tetrad .bz-task-actions .bz-btn-text { margin-left: auto; }
.bz-skin-tetrad .bz-answer-panel, .bz-skin-tetrad .bz-report, .bz-skin-tetrad .bz-explain { margin: 0 22px 16px; }
.bz-skin-tetrad .bz-answer-panel { background: var(--bz-ok-bg); color: var(--bz-ok-ink); font-family: var(--bz-hand); font-size: 26px; padding: 6px 16px; }
/* подсказка и решение — мелом на доске */
.bz-skin-tetrad .bz-explain { border: 8px solid var(--bz-wood); border-radius: 4px; background: var(--bz-board); color: var(--bz-board-ink); padding: 16px 20px; }
.bz-skin-tetrad .bz-explain-t { font-family: var(--bz-chalk); font-weight: 400; font-size: 24px; color: var(--bz-board-acc); }
.bz-skin-tetrad .bz-explain, .bz-skin-tetrad .bz-explain p, .bz-skin-tetrad .bz-explain li { font-size: 18px; line-height: 1.6; }
.bz-skin-tetrad .bz-explain a { color: var(--bz-board-acc); }
.bz-skin-tetrad .bz-explain-by { color: var(--bz-board-mute); }
.bz-skin-tetrad .bz-explain .katex { color: var(--bz-board-ink); }
.bz-skin-tetrad .bz-explain img { background: #FFFFFF; border-radius: 4px; padding: 4px; }

/* сложность — точки */
.bz-skin-tetrad .bz-diff-bars i { width: 9px; height: 9px; border-radius: 50%; }

/* ---------- Номера / строки задач ---------- */
.bz-skin-tetrad .bz-num, .bz-skin-tetrad .bz-trow-n, .bz-skin-tetrad .bz-task-n { border-radius: 2px; }
.bz-skin-tetrad .bz-line { border-radius: var(--bz-radius-sm); }
.bz-skin-tetrad .bz-line-n { font-family: var(--bz-hand); font-weight: 700; font-size: 26px; color: var(--bz-red); }

/* ---------- Репетитор ---------- */
.bz-skin-tetrad .bz-tutor-n { font-family: var(--bz-hand); font-size: 26px; }
.bz-skin-tetrad .bz-tutor-g { font-family: var(--bz-hand); font-size: 22px; }
.bz-skin-tetrad .bz-tutor-g li::before { content: "✓"; background: none; box-shadow: none; color: var(--bz-ok); width: auto; height: auto; margin: 0; font-family: var(--bz-font); font-size: 16px; }

/* ---------- Формы и вход ---------- */
.bz-skin-tetrad .bz-auth-card { border-top: 3px solid var(--bz-red); }

@media (max-width: 760px) {
  .bz-skin-tetrad .bz-task > * { padding-left: 14px; padding-right: 14px; }
  .bz-skin-tetrad .bz-answer-panel, .bz-skin-tetrad .bz-report, .bz-skin-tetrad .bz-explain { margin-left: 12px; margin-right: 12px; }
  .bz-skin-tetrad .bz-brand { font-size: 30px; }
}
html[data-theme="dark"] .bz-skin-tetrad .bz-nav-cta, html[data-theme="dark"] .bz-skin-tetrad .bz-btn-red { color: #2A0B0A !important; }