/* «Математика на полях» — тетрадь в клетку (светлая тема) и школьная доска (тёмная). */

:root {
  --paper: #F9FAF7;
  --grid: rgba(60, 110, 185, 0.11);
  --ink: #18213D;
  --ink-soft: #4B5572;
  --pen: #2447C8;
  --red: #C42D3D;
  --green: #1E8556;
  --amber: #B97F00;
  --violet: #7238B0;
  --card: #FFFFFF;
  --line: #D3DAE6;
  --tint-pen: rgba(36, 71, 200, 0.07);
  --tint-red: rgba(196, 45, 61, 0.07);
  --tint-green: rgba(30, 133, 86, 0.08);
  --focus: #2447C8;

  --f-body: "Literata", Georgia, serif;
  --f-ui: "Golos Text", system-ui, sans-serif;
  --f-hand: "Caveat", "Segoe Print", cursive;
  --f-mono: ui-monospace, "SF Mono", Menlo, monospace;

  --measure: 720px;
  --margin-col: 210px;
  --cell: 24px;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #1C2A26;
    --grid: rgba(255, 255, 255, 0.045);
    --ink: #ECF0E8;
    --ink-soft: #AEBDB5;
    --pen: #93B4FF;
    --red: #FF8F8F;
    --green: #7FDBA9;
    --amber: #F3C85E;
    --violet: #CDA7FF;
    --card: #223430;
    --line: #3B4F48;
    --tint-pen: rgba(147, 180, 255, 0.09);
    --tint-red: rgba(255, 143, 143, 0.08);
    --tint-green: rgba(127, 219, 169, 0.08);
    --focus: #93B4FF;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --paper: #1C2A26;
  --grid: rgba(255, 255, 255, 0.045);
  --ink: #ECF0E8;
  --ink-soft: #AEBDB5;
  --pen: #93B4FF;
  --red: #FF8F8F;
  --green: #7FDBA9;
  --amber: #F3C85E;
  --violet: #CDA7FF;
  --card: #223430;
  --line: #3B4F48;
  --tint-pen: rgba(147, 180, 255, 0.09);
  --tint-red: rgba(255, 143, 143, 0.08);
  --tint-green: rgba(127, 219, 169, 0.08);
  --focus: #93B4FF;
  color-scheme: dark;
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background-color: var(--paper);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: var(--cell) var(--cell);
  color: var(--ink);
  font-family: var(--f-body);
  font-size: 18px;
  line-height: 1.68;
  font-optical-sizing: auto;
}

a { color: var(--pen); text-underline-offset: 3px; text-decoration-thickness: 1px; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: 2.5px solid var(--focus); outline-offset: 2px; border-radius: 3px; }

/* ---------- верхняя полоса ---------- */
.topbar {
  display: flex; align-items: center; justify-content: space-between; gap: 16px;
  padding: 12px 24px;
  font-family: var(--f-ui); font-size: 15px;
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: blur(6px);
  position: sticky; top: 0; z-index: 10;
}
.topbar .brand { color: var(--ink); text-decoration: none; font-weight: 600; }
.topbar .brand span { font-family: var(--f-hand); font-weight: 600; font-size: 22px; color: var(--red); margin-left: 4px; }
.topbar .tools { display: flex; gap: 12px; align-items: center; }
.theme-toggle {
  font: inherit; color: var(--ink-soft); background: none; border: 1px solid var(--line);
  border-radius: 999px; padding: 4px 12px; cursor: pointer;
}
.theme-toggle:hover { color: var(--ink); border-color: var(--ink-soft); }

/* ---------- страница: поля + текст ---------- */
.page {
  max-width: calc(var(--margin-col) + var(--measure) + 120px);
  margin: 0 auto;
  padding: 48px 24px 96px;
}
article {
  margin-left: var(--margin-col);
  padding-left: 36px;
  border-left: 1.5px solid var(--red);
  max-width: calc(var(--measure) + 36px);
  position: relative;
}

.chapter-no {
  font-family: var(--f-hand); font-size: 30px; color: var(--red);
  margin: 0 0 -6px; line-height: 1.1;
}
h1, h2, h3 { font-family: var(--f-body); color: var(--ink); line-height: 1.2; }
h1 { font-size: clamp(34px, 5vw, 50px); font-weight: 650; letter-spacing: -0.015em; margin: 0 0 20px; }
h2 { font-size: 30px; font-weight: 620; margin: 64px 0 16px; letter-spacing: -0.01em; }
h3 { font-size: 22px; font-weight: 600; margin: 36px 0 10px; }
p { margin: 0 0 18px; }
.lede { font-size: 21px; line-height: 1.6; color: var(--ink-soft); margin-bottom: 32px; }
strong { font-weight: 650; }
em { font-style: italic; }
ul, ol { padding-left: 1.3em; margin: 0 0 18px; }
li { margin-bottom: 6px; }
code { font-family: var(--f-mono); font-size: 0.86em; background: var(--tint-pen); padding: 1px 5px; border-radius: 4px; }
pre { font-family: var(--f-mono); font-size: 14px; line-height: 1.5; background: var(--card); border: 1px solid var(--line); border-radius: 6px; padding: 14px 16px; overflow-x: auto; }
pre code { background: none; padding: 0; }
hr { border: 0; border-top: 1px dashed var(--line); margin: 48px 0; }
.katex { font-size: 1.06em; }
.katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }

/* ---------- заметки на полях (рукописные, красной ручкой) ---------- */
.note {
  float: left; clear: left;
  width: calc(var(--margin-col) - 24px);
  margin-left: calc(-1 * (var(--margin-col) + 36px));
  margin-top: 4px;
  font-family: var(--f-hand); font-size: 21px; line-height: 1.2; color: var(--red);
  transform: rotate(-1.6deg);
  text-align: right;
  padding-right: 10px;
}
.note.blue { color: var(--pen); }
.note .katex { font-size: 0.9em; }

/* ---------- врезки ---------- */
.box { margin: 28px 0; padding: 18px 22px; border-radius: 4px 10px 10px 4px; background: var(--card); border: 1px solid var(--line); }
.box > :last-child { margin-bottom: 0; }
.box-title { font-family: var(--f-hand); font-size: 26px; line-height: 1; margin: 0 0 10px; font-weight: 600; }

details.likbez { border-left: 4px solid var(--pen); }
details.likbez > summary { cursor: pointer; list-style: none; display: flex; align-items: baseline; gap: 10px; }
details.likbez > summary::-webkit-details-marker { display: none; }
details.likbez > summary .box-title { color: var(--pen); margin: 0; }
details.likbez > summary .sub { font-family: var(--f-ui); font-size: 15px; color: var(--ink-soft); }
details.likbez > summary::after { content: "+"; margin-left: auto; font-family: var(--f-ui); color: var(--pen); font-size: 20px; }
details.likbez[open] > summary::after { content: "−"; }
details.likbez[open] > summary { margin-bottom: 12px; }

.insight { border-left: 4px solid var(--red); background: var(--tint-red); }
.insight .box-title { color: var(--red); }
.insight p { font-size: 19px; }

.assembler { border-left: 4px solid var(--green); background: var(--tint-green); }
.assembler .box-title { color: var(--green); }

.exercise { border-left: 4px solid var(--amber); }
.exercise .box-title { color: var(--amber); }
.exercise details { margin-top: 8px; }
.exercise details > summary { cursor: pointer; font-family: var(--f-ui); font-size: 15px; color: var(--ink-soft); }
.exercise details[open] > summary { margin-bottom: 6px; }

/* ---------- виджеты ---------- */
.widget {
  margin: 32px 0; background: var(--card);
  border: 1.5px solid var(--ink); border-radius: 8px;
  font-family: var(--f-ui); font-size: 15px; line-height: 1.45;
  overflow: hidden;
}
.widget-head { display: flex; align-items: baseline; gap: 12px; padding: 12px 16px 0; }
.widget-title { font-weight: 600; font-size: 16px; margin: 0; }
.widget-hint { color: var(--ink-soft); font-size: 14px; }
.widget-stage { padding: 12px 16px; display: flex; flex-wrap: wrap; gap: 16px; align-items: flex-start; justify-content: center; }
.widget-stage svg { display: block; max-width: 100%; height: auto; touch-action: none; user-select: none; -webkit-user-select: none; }
.widget-controls { display: flex; flex-wrap: wrap; gap: 10px 18px; align-items: center; padding: 10px 16px 14px; border-top: 1px dashed var(--line); }
.widget-readout { padding: 10px 16px 14px; border-top: 1px dashed var(--line); color: var(--ink-soft); min-height: 1.45em; }
.widget-readout b { color: var(--ink); font-weight: 600; }
.widget-caption { font-family: var(--f-ui); font-size: 14px; color: var(--ink-soft); margin: -20px 0 28px; }

.ctl { display: inline-flex; align-items: center; gap: 8px; }
.ctl label, .ctl .ctl-label { color: var(--ink-soft); white-space: nowrap; }
.ctl output { min-width: 3.2em; font-variant-numeric: tabular-nums; color: var(--ink); font-weight: 600; }
.ctl input[type="range"] { width: 130px; accent-color: var(--pen); }

.btn {
  font: inherit; font-weight: 550; cursor: pointer;
  color: var(--ink); background: var(--paper);
  border: 1.5px solid var(--ink); border-radius: 6px; padding: 6px 14px;
}
.btn:hover { background: var(--tint-pen); }
.btn.primary { background: var(--pen); color: var(--card); border-color: var(--pen); }
.btn.primary:hover { filter: brightness(1.08); }
.btn:disabled { opacity: 0.45; cursor: default; }

.seg { display: inline-flex; border: 1.5px solid var(--ink); border-radius: 6px; overflow: hidden; }
.seg button { font: inherit; border: 0; background: var(--paper); color: var(--ink); padding: 5px 12px; cursor: pointer; border-right: 1px solid var(--line); }
.seg button:last-child { border-right: 0; }
.seg button[aria-pressed="true"] { background: var(--ink); color: var(--paper); }

/* матрица в квадратных скобках */
.mat { display: inline-grid; position: relative; padding: 4px 10px; gap: 2px 6px; font-family: var(--f-ui); font-variant-numeric: tabular-nums; vertical-align: middle; }
.mat::before, .mat::after { content: ""; position: absolute; top: 0; bottom: 0; width: 7px; border: 1.8px solid var(--ink); }
.mat::before { left: 0; border-right: 0; }
.mat::after { right: 0; border-left: 0; }
.mat .c { min-width: 2.2em; text-align: center; padding: 2px 4px; border-radius: 4px; transition: background 0.15s; }
.mat .c.hl { background: var(--tint-pen); outline: 1.5px solid var(--pen); }
.mat .c.hl2 { background: var(--tint-red); outline: 1.5px solid var(--red); }
.mat .c.zero { color: var(--ink-soft); opacity: 0.5; }
.mat input.c { width: 3.4em; font: inherit; color: var(--ink); background: var(--paper); border: 1px solid var(--line); }

.legend { display: flex; flex-wrap: wrap; gap: 6px 16px; color: var(--ink-soft); font-size: 14px; }
.legend i { display: inline-block; width: 12px; height: 12px; border-radius: 3px; vertical-align: -1px; margin-right: 6px; }

/* svg-классы, чтобы цвета менялись с темой */
.sv-ink { stroke: var(--ink); }
.sv-soft { stroke: var(--ink-soft); }
.sv-grid { stroke: var(--line); }
.sv-text { fill: var(--ink); font-family: var(--f-ui); }
.sv-text-soft { fill: var(--ink-soft); font-family: var(--f-ui); }
.sv-hand { fill: var(--red); font-family: var(--f-hand); }

/* ---------- навигация по главам ---------- */
.chapter-nav { display: flex; justify-content: space-between; gap: 16px; margin-top: 80px; padding-top: 24px; border-top: 1.5px solid var(--ink); font-family: var(--f-ui); }
.chapter-nav a { text-decoration: none; display: block; max-width: 45%; }
.chapter-nav a small { display: block; color: var(--ink-soft); font-size: 14px; }
.chapter-nav a span { font-size: 17px; font-weight: 550; }
.chapter-nav a.next { text-align: right; margin-left: auto; }

/* ---------- оглавление (главная) ---------- */
.hero h1 { font-size: clamp(40px, 7vw, 68px); margin-bottom: 12px; }
.hero .lede { max-width: 36em; }
.hero-demo { margin-top: 28px; }
.toc-part { margin-top: 56px; }
.toc-part h2 { margin: 0 0 6px; font-size: 26px; }
.toc-part > p { color: var(--ink-soft); }
.toc { list-style: none; padding: 0; margin: 16px 0 0; counter-reset: none; }
.toc li { display: grid; grid-template-columns: 52px 1fr; gap: 4px 12px; padding: 12px 0; border-bottom: 1px dashed var(--line); margin: 0; }
.toc .num { font-family: var(--f-hand); font-size: 30px; color: var(--red); line-height: 1; }
.toc a { font-size: 20px; font-weight: 600; text-decoration: none; }
.toc a:hover { text-decoration: underline; }
.toc .desc { grid-column: 2; color: var(--ink-soft); font-size: 16px; line-height: 1.5; }
.toc .soon { color: var(--ink-soft); font-weight: 500; }

footer.site { font-family: var(--f-ui); font-size: 14px; color: var(--ink-soft); text-align: center; padding: 24px; }

/* ---------- узкие экраны ---------- */
@media (max-width: 1000px) {
  article { margin-left: 0; padding-left: 20px; }
  .note {
    float: none; width: auto; margin: 0 0 16px; transform: none; text-align: left;
    padding: 2px 0 2px 12px; border-left: 2px solid currentColor;
  }
}
@media (max-width: 600px) {
  body { font-size: 17px; }
  .page { padding: 28px 16px 72px; }
  article { padding-left: 14px; }
  .topbar { padding: 10px 16px; }
  h2 { font-size: 25px; margin-top: 48px; }
  .lede { font-size: 19px; }
  .box { padding: 14px 16px; }
  .widget-stage, .widget-controls, .widget-readout { padding-left: 12px; padding-right: 12px; }
  .widget-head { padding: 12px 12px 0; flex-wrap: wrap; }
  .ctl input[type="range"] { width: 110px; }
  .chapter-nav a { max-width: 48%; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; animation: none !important; scroll-behavior: auto !important; }
}