/* Course theme. Ink and paper with one accent (campus gold), flat colour, no gradients.
   Typeface: IBM Plex Sans (full Cyrillic) with heavy display headings and regular body. */

@font-face { font-family: "IBM Plex Sans"; font-weight: 400; font-style: normal; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-sans-cyrillic-400-normal.7dec1409f343.woff2") format("woff2");
  unicode-range: U+0301, U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116; }
@font-face { font-family: "IBM Plex Sans"; font-weight: 400; font-style: normal; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-sans-latin-400-normal.77bc02670657.woff2") format("woff2");
  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD; }
@font-face { font-family: "IBM Plex Sans"; font-weight: 400; font-style: italic; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-sans-cyrillic-400-italic.eaaacc51140d.woff2") format("woff2");
  unicode-range: U+0301, U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116; }
@font-face { font-family: "IBM Plex Sans"; font-weight: 400; font-style: italic; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-sans-latin-400-italic.ac3e6cdbce96.woff2") format("woff2");
  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD; }
@font-face { font-family: "IBM Plex Sans"; font-weight: 700; font-style: normal; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-sans-cyrillic-700-normal.fe1b8353cdd7.woff2") format("woff2");
  unicode-range: U+0301, U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116; }
@font-face { font-family: "IBM Plex Sans"; font-weight: 700; font-style: normal; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-sans-latin-700-normal.c277d7b83f8a.woff2") format("woff2");
  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD; }
@font-face { font-family: "IBM Plex Sans"; font-weight: 700; font-style: italic; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-sans-cyrillic-700-italic.e298fbb86db5.woff2") format("woff2");
  unicode-range: U+0301, U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116; }
@font-face { font-family: "IBM Plex Mono"; font-weight: 400; font-style: normal; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-mono-cyrillic-400-normal.2f3900b11191.woff2") format("woff2");
  unicode-range: U+0301, U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116; }
@font-face { font-family: "IBM Plex Mono"; font-weight: 400; font-style: normal; font-display: swap;
  src: url("../vendor/fonts/ibm-plex-mono-latin-400-normal.79936b18df9f.woff2") format("woff2");
  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD; }

:root {
  --paper: #F8F8F8;
  --white: #FFFFFF;
  --ink: #141414;
  --ink-2: #474747;
  --rule: #D4D4D4;
  --rule-2: #E8E8E8;
  --muted: #8C8C8C;
  --gold: #B8913A;
  --gold-ink: #7A5C1E;
  --gold-soft: #EFE3C8;
  --blue: #3E5C76;
  --blue-soft: #D8E0E8;
  --bad: #A33A2B;
  --bad-soft: #F2DCD8;
  --font: "IBM Plex Sans", "Helvetica Neue", Arial, sans-serif;
  --mono: "IBM Plex Mono", "SFMono-Regular", Menlo, monospace;
  --text: 20px;
  --lh: 1.62;
  --col: 46rem;        /* reading column, ~760px at 16px root */
  --gutter: 24px;
  --radius: 2px;
}
@media (max-width: 700px) {
  :root { --text: 18px; --gutter: 16px; }
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: 72px; }
body { margin: 0; background: var(--paper); color: var(--ink); font: 400 var(--text)/var(--lh) var(--font);
  -webkit-font-smoothing: antialiased; text-rendering: optimizeLegibility; }
img, svg { max-width: 100%; }
a { color: var(--ink); text-decoration-color: var(--gold); text-decoration-thickness: 2px; text-underline-offset: 3px; }
a:hover { text-decoration-color: var(--ink); }
:focus-visible { outline: 3px solid var(--gold); outline-offset: 2px; }
[hidden] { display: none !important; }
.visually-hidden { position: absolute !important; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
.skip { position: absolute; left: -999px; top: 0; background: var(--ink); color: var(--white); padding: 8px 12px; z-index: 100; }
.skip:focus { left: 8px; }
h1, h2, h3, h4 { font-weight: 700; line-height: 1.18; letter-spacing: -0.01em; margin: 0; }
code { font-family: var(--mono); font-size: .88em; background: var(--rule-2); padding: 1px 4px; border-radius: var(--radius); }
small { font-size: .82em; color: var(--ink-2); }

/* ---- header ---------------------------------------------------------------------------- */
.site-header { background: var(--paper); border-bottom: 1px solid var(--ink); position: sticky; top: 0; z-index: 20; }
.site-header__in { max-width: 1240px; margin: 0 auto; padding: 0 var(--gutter); display: flex; align-items: center;
  justify-content: space-between; gap: 16px; min-height: 56px; }
.wordmark { font-weight: 700; font-size: 17px; text-decoration: none; letter-spacing: -0.005em; line-height: 1.2; }
.site-nav__menu { position: relative; }
.site-nav__menu summary { list-style: none; cursor: pointer; font-size: 16px; padding: 8px 12px; border: 1.5px solid var(--ink);
  border-radius: var(--radius); user-select: none; }
.site-nav__menu summary::-webkit-details-marker { display: none; }
.site-nav__menu ul { list-style: none; margin: 0; padding: 8px 0; position: absolute; right: 0; top: calc(100% + 8px);
  background: var(--white); border: 1.5px solid var(--ink); min-width: 220px; }
.site-nav__menu li a, .site-nav__menu li button { display: block; padding: 8px 16px; font-size: 16px; text-decoration: none; width: 100%; text-align: left; }
.site-nav__menu li a:hover, .site-nav__menu li button:hover { background: var(--paper); }
.site-nav__list { display: none; list-style: none; margin: 0; padding: 0; gap: 2px; }
.site-nav__list a, .site-nav__list button { display: block; padding: 6px 10px; font-size: 16px; text-decoration: none; }
.site-nav__list a:hover, .site-nav__list button:hover { text-decoration: underline; text-decoration-color: var(--gold); }
.site-nav__list form { margin: 0; }
@media (min-width: 900px) {
  .site-nav__list { display: flex; }
  .site-nav__menu { display: none; }
}
.linklike { background: none; border: 0; padding: 0; font: inherit; color: inherit; cursor: pointer; text-decoration: underline;
  text-decoration-color: var(--gold); text-decoration-thickness: 2px; text-underline-offset: 3px; }

/* ---- editor bar --------------------------------------------------------------------------- */
.editbar { background: var(--ink); color: var(--white); font-size: 15px; }
.editbar__in { max-width: 1240px; margin: 0 auto; padding: 6px var(--gutter); display: flex; flex-wrap: wrap; gap: 8px 16px; align-items: center; }
.editbar form { margin: 0; }
.editbar__btn { color: var(--white); background: none; border: 1px solid #777; border-radius: var(--radius); padding: 4px 10px; font: inherit; cursor: pointer; text-decoration: none; }
.editbar__btn[aria-pressed=true] { background: var(--gold); color: var(--ink); border-color: var(--gold); }
.editbar__note { color: var(--gold-soft); }
.editbar__who { color: #BDBDBD; }

.messages { max-width: 1240px; margin: 12px auto 0; padding: 0 var(--gutter); }
.message { margin: 0 0 8px; padding: 10px 14px; border-left: 4px solid var(--ink); background: var(--white); font-size: 17px; }
.message.success { border-left-color: var(--gold); }
.message.error { border-left-color: var(--bad); background: var(--bad-soft); }
.message.warning { border-left-color: var(--gold); background: var(--gold-soft); }

/* ---- buttons, inputs, tags ------------------------------------------------------------------ */
.btn { display: inline-flex; align-items: center; gap: 8px; font: 700 17px/1 var(--font); padding: 13px 20px; border: 1.5px solid var(--ink);
  background: var(--white); color: var(--ink); border-radius: var(--radius); cursor: pointer; text-decoration: none; }
.btn:hover { background: var(--paper); }
.btn--primary { background: var(--ink); color: var(--white); }
.btn--primary:hover { background: #333; }
.btn--quiet { border-color: transparent; background: none; text-decoration: underline; text-decoration-color: var(--gold);
  text-decoration-thickness: 2px; text-underline-offset: 4px; font-weight: 400; padding-left: 4px; padding-right: 4px; }
.btn--quiet:hover { background: none; text-decoration-color: var(--ink); }
.btn--small { font-size: 14px; padding: 7px 11px; }
.btn:disabled { opacity: .45; cursor: default; }
.input { font: 400 18px var(--font); padding: 9px 11px; border: 1.5px solid var(--ink-2); border-radius: var(--radius); background: var(--white);
  color: var(--ink); max-width: 100%; }
.input:focus { outline: 3px solid var(--gold); outline-offset: 0; border-color: var(--ink); }
.input--num { font-family: var(--mono); width: 11em; font-size: 20px; }
.input--code { font-family: var(--mono); letter-spacing: .12em; text-transform: uppercase; }
textarea.input { width: 100%; font-size: 16px; }
.tag { display: inline-block; font-size: 13px; line-height: 1; padding: 4px 6px; border: 1px solid var(--ink-2); border-radius: var(--radius); color: var(--ink-2); vertical-align: middle; font-weight: 400; }
.tag--draft { border-color: var(--gold); background: var(--gold-soft); color: var(--gold-ink); }

/* ---- home ------------------------------------------------------------------------------------ */
.hero { max-width: 1240px; margin: 0 auto; padding: 64px var(--gutter) 48px; display: grid; grid-template-columns: 7fr 5fr; gap: 48px; align-items: center; }
.hero h1 { font-size: clamp(40px, 6vw, 72px); line-height: 1.02; letter-spacing: -0.025em; max-width: 12ch; }
.hero__sub { font-size: 24px; line-height: 1.4; margin: 24px 0 0; max-width: 30ch; }
.hero__desc { color: var(--ink-2); margin: 20px 0 0; max-width: 40rem; }
.hero__actions { margin: 32px 0 0; }
.hero__art { margin: 0; justify-self: end; width: 100%; max-width: 520px; }
.hero__art svg { display: block; width: 100%; height: auto; }
@media (max-width: 860px) {
  .hero { grid-template-columns: 1fr; padding-top: 40px; gap: 24px; }
  .hero__art { order: -1; max-width: 300px; justify-self: start; }
}

.lessons { max-width: 1240px; margin: 0 auto; padding: 24px var(--gutter) 80px; display: grid; grid-template-columns: 3fr 9fr; gap: 0 48px; }
.lessons__title { font-size: 32px; padding-top: 22px; border-top: 6px solid var(--ink); }
.lesson-list { list-style: none; margin: 0; padding: 0; border-top: 6px solid var(--ink); }
.lesson-list__part { font-size: 15px; font-weight: 700; text-transform: uppercase; letter-spacing: .02em; padding: 28px 0 10px; color: var(--ink); border-bottom: 1px solid var(--ink); }
.lesson-list__part:first-child { padding-top: 18px; }
.lesson-row { display: grid; grid-template-columns: 3.2rem 1fr 9rem; gap: 20px; padding: 20px 0 22px; border-bottom: 1px solid var(--rule); align-items: start; }
.lesson-row__num { font-size: 32px; font-weight: 700; line-height: 1; color: var(--ink); font-variant-numeric: tabular-nums; }
.lesson-row h3 { font-size: 24px; line-height: 1.22; }
.lesson-row h3 a { text-decoration: none; }
.lesson-row h3 a:hover { text-decoration: underline; text-decoration-color: var(--gold); }
.lesson-row p { margin: 6px 0 0; font-size: 18px; color: var(--ink-2); }
.lesson-row__progress { padding-top: 8px; font-size: 15px; color: var(--ink-2); }
.lesson-row.is-hidden { opacity: .55; }
.meter { display: block; height: 6px; background: var(--rule-2); margin-bottom: 6px; }
.meter__fill { display: block; height: 100%; background: var(--gold); }
.lesson-row.is-done .meter__fill { background: var(--ink); }
@media (max-width: 860px) {
  .lessons { grid-template-columns: 1fr; }
  .lessons__title { border-top: 0; padding-top: 0; margin-bottom: 8px; }
  .lesson-row { grid-template-columns: 2.4rem 1fr; }
  .lesson-row__num { font-size: 24px; }
  .lesson-row__progress { grid-column: 2; padding-top: 0; }
  .lesson-row h3 { font-size: 21px; }
}

/* ---- lesson layout ---------------------------------------------------------------------------- */
.lesson-layout { max-width: 1240px; margin: 0 auto; padding: 0 var(--gutter); display: grid; grid-template-columns: 15rem minmax(0, var(--col)); gap: 56px; }
.lesson-toc { padding-top: 48px; }
.lesson-toc__in { position: sticky; top: 80px; max-height: calc(100vh - 100px); overflow: auto; }
.lesson-toc__num { margin: 0; font-size: 15px; color: var(--ink-2); }
.lesson-toc__title { margin: 2px 0 16px; font-weight: 700; font-size: 18px; line-height: 1.3; }
.toc { list-style: none; margin: 0; padding: 0; border-top: 1px solid var(--ink); }
.toc a { display: flex; gap: 10px; align-items: baseline; padding: 9px 0; border-bottom: 1px solid var(--rule); text-decoration: none; font-size: 16px; line-height: 1.35; }
.toc a:hover { color: var(--gold-ink); }
.toc__mark { flex: 0 0 10px; width: 10px; height: 10px; border: 1.5px solid var(--ink); transform: translateY(1px); }
.toc a.is-done .toc__mark { background: var(--ink); }
.toc a.is-started .toc__mark { background: var(--gold); border-color: var(--gold); }
.toc a.is-current { font-weight: 700; }
.lesson-toc__progress { font-size: 15px; color: var(--ink-2); margin: 14px 0 6px; }
.lesson-toc__all { font-size: 15px; }
@media (max-width: 1000px) {
  .lesson-layout { grid-template-columns: minmax(0, 1fr); gap: 0; }
  .lesson-toc { padding-top: 24px; }
  .lesson-toc__in { position: static; max-height: none; }
  .lesson-toc .toc { display: none; }
  .lesson-toc__title { display: none; }
}

.lesson { padding: 48px 0 80px; min-width: 0; }
.lesson-head { padding-bottom: 28px; border-bottom: 6px solid var(--ink); margin-bottom: 8px; }
.lesson-head__num { margin: 0 0 8px; font-size: 18px; color: var(--ink-2); }
.lesson-head h1 { font-size: clamp(36px, 5vw, 56px); line-height: 1.05; letter-spacing: -0.02em; }
.lesson-head__summary { font-size: 22px; line-height: 1.45; margin: 18px 0 0; }

.lsec { padding-top: 48px; }
.lsec + .lsec { margin-top: 24px; border-top: 1px solid var(--ink); }
.lsec__title { font-size: clamp(28px, 3.4vw, 36px); margin-bottom: 20px; }

.step[hidden] { display: none; }
.step__next { margin: 28px 0 8px; }
.step__next[hidden] { display: none; }
.step.is-new { animation: reveal .28s ease-out; }
@keyframes reveal { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }
@media (prefers-reduced-motion: reduce) { .step.is-new { animation: none; } }

/* ---- prose ---------------------------------------------------------------------------------- */
.block { position: relative; margin: 0 0 24px; }
.prose > :first-child { margin-top: 0; }
.prose > :last-child { margin-bottom: 0; }
.prose p { margin: 0 0 18px; }
.prose h3 { font-size: 24px; margin: 36px 0 12px; }
.prose h4 { font-size: 20px; margin: 28px 0 10px; }
.prose ul, .prose ol { margin: 0 0 18px; padding-left: 1.3em; }
.prose li { margin: 0 0 8px; }
.prose li::marker { color: var(--ink-2); }
.prose strong { font-weight: 700; }
.prose blockquote { margin: 0 0 18px; padding: 2px 0 2px 20px; border-left: 4px solid var(--ink); }
.prose table { border-collapse: collapse; margin: 0 0 22px; font-size: 17px; width: 100%; display: block; overflow-x: auto; }
.prose th, .prose td { border-bottom: 1px solid var(--rule); padding: 9px 14px 9px 0; text-align: left; vertical-align: top; }
.prose th { border-bottom: 2px solid var(--ink); font-weight: 700; }
.prose td.ta-right, .prose th.ta-right { text-align: right; font-variant-numeric: tabular-nums; }
.prose td.ta-center, .prose th.ta-center { text-align: center; }
.math-display { display: block; overflow-x: auto; overflow-y: hidden; margin: 6px 0 18px; padding: 4px 0; }
.equation { margin: 8px 0 24px; padding: 18px 0; border-top: 1px solid var(--rule); border-bottom: 1px solid var(--rule); overflow-x: auto; }
.equation .math-display { margin: 0; }
mjx-container[jax="SVG"] { font-size: 104%; }
mjx-container[jax="SVG"][display="true"] { margin: 0 !important; text-align: left !important; }

/* Callouts: flat blocks, distinguished by a left bar and a title */
.admonition { margin: 4px 0 22px; padding: 16px 20px 16px; background: var(--white); border-left: 6px solid var(--ink); }
.admonition-title { font-weight: 700; margin: 0 0 8px !important; font-size: 17px; }
.admonition p:last-child { margin-bottom: 0; }
.admonition.case { border-left-color: var(--blue); }
.admonition.case .admonition-title { color: var(--blue); }
.admonition.numbers { border-left-color: var(--muted); background: var(--paper); border-top: 1px dashed var(--muted); border-right: 1px dashed var(--muted); border-bottom: 1px dashed var(--muted); }
.admonition.math { border-left-color: var(--gold); background: var(--white); }
.admonition.math .admonition-title { color: var(--gold-ink); }
.admonition.key { background: var(--ink); color: var(--white); border-left-color: var(--gold); }
.admonition.key .admonition-title { color: var(--gold); }
.admonition.key mjx-container { color: var(--white); }

.figure { margin: 8px 0 28px; }
.figure img { display: block; width: 100%; height: auto; background: var(--white); border: 1px solid var(--rule); }
.figure figcaption { font-size: 16px; color: var(--ink-2); margin-top: 10px; }

/* ---- exercises --------------------------------------------------------------------------------- */
.ex { background: var(--white); border: 1.5px solid var(--ink); padding: 22px 24px 20px; margin: 8px 0 28px; }
.ex--widget { padding: 20px 0 18px; }
.ex--widget > .ex__label, .ex--widget > .ex__prompt, .ex--widget > .ex__actions, .ex--widget > .ex__feedback,
.ex--widget > .ex__changed { padding-left: 24px; padding-right: 24px; }
.ex__label { margin: 0 0 8px; font-size: 15px; font-weight: 700; color: var(--gold-ink); }
.ex__prompt { margin-bottom: 16px; }
.ex__prompt p { margin-bottom: 12px; }
.ex__options { border: 0; margin: 0 0 16px; padding: 0; display: grid; gap: 8px; }
.opt { display: flex; gap: 12px; align-items: flex-start; padding: 12px 14px; border: 1.5px solid var(--rule); cursor: pointer; border-radius: var(--radius); font-size: 18px; line-height: 1.45; }
.opt:hover { border-color: var(--ink-2); }
.opt input { margin: 4px 0 0; width: 18px; height: 18px; accent-color: var(--ink); flex: 0 0 auto; }
.opt:has(input:checked) { border-color: var(--ink); background: var(--paper); }
.opt.is-right { border-color: var(--gold); background: var(--gold-soft); }
.opt.is-wrong { border-color: var(--bad); background: var(--bad-soft); }
.opt__text p { margin: 0; }
.ex__number { display: flex; flex-wrap: wrap; gap: 10px 14px; align-items: center; margin-bottom: 16px; }
.ex__number-label { font-size: 16px; color: var(--ink-2); width: 100%; }
.ex__unit { font-size: 18px; color: var(--ink-2); }
.input--num.is-right { border-color: var(--gold); background: var(--gold-soft); }
.input--num.is-wrong { border-color: var(--bad); background: var(--bad-soft); }
.ex__widget { margin: 0 0 14px; border-top: 1px solid var(--rule); border-bottom: 1px solid var(--rule); }
.ex__widget iframe { display: block; width: 100%; border: 0; background: var(--white); }
.ex__actions { display: flex; flex-wrap: wrap; gap: 10px 16px; align-items: center; }
.ex__status { font-size: 16px; color: var(--ink-2); }
.ex__status.is-done { color: var(--ink); font-weight: 700; }
.ex__status.is-done::before { content: ""; display: inline-block; width: 10px; height: 10px; background: var(--gold); margin-right: 8px; }
.ex__feedback:empty { display: none; }
.ex__feedback { margin-top: 14px; }
.fb { padding: 12px 16px; border-left: 5px solid var(--rule); background: var(--paper); font-size: 18px; }
.fb + .fb { margin-top: 8px; }
.fb p { margin: 0 0 8px; } .fb p:last-child { margin: 0; }
.fb--good { border-left-color: var(--gold); background: var(--gold-soft); }
.fb--bad { border-left-color: var(--bad); background: var(--bad-soft); }
.fb__head { font-weight: 700; display: block; margin-bottom: 4px; }
.ex__explanation { margin-top: 16px; padding-top: 16px; border-top: 1px solid var(--rule); }
.ex__explanation::before { content: "Решение"; display: block; font-weight: 700; font-size: 16px; margin-bottom: 8px; color: var(--ink-2); }
.ex__changed { margin: 12px 0 0; font-size: 15px; color: var(--gold-ink); }
@media (max-width: 700px) {
  .ex { padding: 18px 16px 16px; margin-left: calc(-1 * var(--gutter) + 4px); margin-right: calc(-1 * var(--gutter) + 4px); }
  .ex--widget { padding: 16px 0; }
  .ex--widget > .ex__label, .ex--widget > .ex__prompt, .ex--widget > .ex__actions, .ex--widget > .ex__feedback { padding-left: 16px; padding-right: 16px; }
}

.quiz { margin-top: 40px; padding: 28px 0 0; border-top: 6px solid var(--ink); }
.quiz__title { font-size: 26px; }
.quiz__score { margin: 6px 0 18px; font-size: 17px; color: var(--ink-2); }
.ex--quiz { border-width: 1px; border-color: var(--rule); }

.lesson-pager { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin-top: 72px; border-top: 6px solid var(--ink); padding-top: 20px; }
.lesson-pager a { text-decoration: none; font-weight: 700; font-size: 19px; line-height: 1.3; }
.lesson-pager a span { display: block; font-weight: 400; font-size: 15px; color: var(--ink-2); margin-bottom: 4px; }
.lesson-pager__next { text-align: right; }
@media (max-width: 600px) { .lesson-pager { grid-template-columns: 1fr; } .lesson-pager__next { text-align: left; } }

/* ---- editor tools on lesson pages --------------------------------------------------------------- */
.btools { display: none; }
.is-editor .btools { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; margin: 0 0 6px; font-size: 13px; opacity: .45; transition: opacity .15s; }
.is-editor .block:hover > .btools, .is-editor .hero__head:hover > .btools, .is-editor .lesson-head:hover > .btools,
.is-editor .lsec__head:hover > .btools, .is-editor .btools:focus-within { opacity: 1; }
.btools__btn { font: 400 13px var(--font); padding: 3px 8px; border: 1px solid var(--ink-2); background: var(--white); color: var(--ink); cursor: pointer; border-radius: var(--radius); text-decoration: none; line-height: 1.4; list-style: none; }
.btools__btn::-webkit-details-marker { display: none; }
.btools__btn--danger { border-color: var(--bad); color: var(--bad); }
.btools__inline { display: inline-flex; gap: 4px; margin: 0; }
.btools__check { display: inline-flex; gap: 6px; align-items: center; font-size: 14px; }
.tools-pop { position: relative; display: inline-block; }
.tools-pop[open] > form, .tools-pop[open] > .add-block__form { position: absolute; z-index: 10; background: var(--white); border: 1.5px solid var(--ink); padding: 12px; width: 320px; display: grid; gap: 8px; font-size: 15px; }
.tools-pop label { display: grid; gap: 4px; }
.flag-msg { margin: 0; font-size: 14px; }
.add-block { margin-top: 16px; opacity: .6; }
.add-block:hover, .add-block[open] { opacity: 1; }
.lsec__rename { margin: -8px 0 16px; font-size: 14px; }
.lsec__rename[open] form { display: flex; gap: 8px; width: auto; }
.block.is-draft, .lsec__head.is-draft, .lesson-head.is-draft, .hero__head.is-draft { outline: 2px dashed var(--gold); outline-offset: 8px; }
.lsec__head .btools, .lesson-head .btools, .hero__head .btools { margin-bottom: 8px; }
.deleted-note { font-size: 15px; color: var(--bad); border: 1px dashed var(--bad); padding: 8px 12px; margin: 0; }

.block--editing { background: var(--white); border: 2px solid var(--ink); padding: 16px; margin: 0 -18px 28px; }
.bedit { display: grid; gap: 14px; }
.bedit__title { margin: 0; font-weight: 700; font-size: 16px; }
.bedit__errors { margin: 0; padding: 10px 14px 10px 30px; background: var(--bad-soft); border-left: 4px solid var(--bad); font-size: 15px; }
.bedit__pair { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; align-items: start; }
.bedit__field { display: grid; gap: 6px; font-size: 14px; color: var(--ink-2); }
.bedit__preview { border: 1px dashed var(--rule); padding: 10px 12px; font-size: 17px; min-height: 60px; background: var(--paper); overflow: auto; }
.bedit__preview:empty::before { content: "Предпросмотр"; color: var(--muted); font-size: 14px; }
.bedit__row { display: flex; flex-wrap: wrap; gap: 12px; align-items: end; font-size: 14px; }
.bedit__row label { display: grid; gap: 4px; }
.bedit__options, .bedit__params { border: 1px solid var(--rule); padding: 10px 12px; display: grid; gap: 8px; font-size: 14px; }
.bedit__opt { display: grid; grid-template-columns: auto 1fr 1fr; gap: 8px; align-items: start; }
.bedit__param { display: grid; gap: 4px; }
.bedit__actions { display: flex; gap: 10px; }
.bedit__img { max-height: 200px; width: auto; border: 1px solid var(--rule); }
.bedit .cm-editor { border: 1.5px solid var(--ink-2); background: var(--white); font-size: 14px; max-height: 480px; }
.bedit .cm-editor.cm-focused { outline: 3px solid var(--gold); }
@media (max-width: 800px) { .bedit__pair { grid-template-columns: 1fr; } .block--editing { margin: 0 0 28px; } }

/* ---- tool pages (history, QA, widgets, exam) ------------------------------------------------- */
.tool { max-width: 1000px; margin: 0 auto; padding: 40px var(--gutter) 80px; }
.tool--narrow { max-width: 640px; }
.tool--wide { max-width: 1240px; }
.tool h1 { font-size: clamp(30px, 4vw, 44px); margin-bottom: 12px; }
.tool h2 { font-size: 24px; margin: 28px 0 10px; }
.tool__back { font-size: 16px; margin: 0 0 16px; }
.tool__lead { color: var(--ink-2); margin: 0 0 24px; }
.tool__note { font-size: 15px; color: var(--ink-2); }
.prose-page p { max-width: 42rem; }
.table { width: 100%; border-collapse: collapse; font-size: 16px; margin: 0 0 20px; }
.table th, .table td { text-align: left; vertical-align: top; padding: 10px 12px 10px 0; border-bottom: 1px solid var(--rule); }
.table th { border-bottom: 2px solid var(--ink); font-size: 15px; }
.table__actions { white-space: nowrap; }
.table__actions .btn { margin: 0 4px 4px 0; }
.filters { display: flex; flex-wrap: wrap; gap: 12px; align-items: end; margin: 0 0 24px; font-size: 15px; }
.filters label { display: grid; gap: 4px; }
.form-stack { display: grid; gap: 14px; margin: 16px 0; }
.form-stack label { display: grid; gap: 6px; font-size: 16px; }
.form-stack--tight { gap: 6px; margin: 0; }
.change-list { margin: 0 0 24px; padding-left: 1.2em; }
.change-list li { margin: 0 0 6px; }
.facts { list-style: none; padding: 0; margin: 16px 0; border-top: 1px solid var(--ink); }
.facts li { padding: 8px 0; border-bottom: 1px solid var(--rule); }
.diff { overflow-x: auto; background: var(--white); border: 1px solid var(--rule); }
.diff table.diff { font-family: var(--mono); font-size: 13px; border-collapse: collapse; width: 100%; }
.diff td { padding: 1px 6px; vertical-align: top; white-space: pre-wrap; word-break: break-word; }
.diff .diff_header { color: var(--muted); }
.diff .diff_add { background: var(--gold-soft); }
.diff .diff_chg { background: #F5EBD3; }
.diff .diff_sub { background: var(--bad-soft); }
.history-compare input[type=radio] { width: 16px; height: 16px; accent-color: var(--ink); }
.usage ul { padding-left: 1.2em; font-size: 16px; }
.usage li { margin: 0 0 8px; }
.wedit { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 24px; margin-top: 24px; align-items: start; }
.wedit__form { display: grid; gap: 14px; }
.wedit__preview { position: sticky; top: 80px; }
.wedit .cm-editor { border: 1.5px solid var(--ink-2); background: var(--white); font-size: 13px; max-height: 560px; }
@media (max-width: 1000px) { .wedit { grid-template-columns: 1fr; } .wedit__preview { position: static; } }

.exam-q { padding: 28px 0; border-bottom: 1px solid var(--rule); }
.exam-q__num { margin: 0 0 10px; font-size: 15px; color: var(--ink-2); font-weight: 700; }
.exam__submit { margin-top: 32px; display: flex; gap: 16px; align-items: center; flex-wrap: wrap; }
.exam-timer { font-family: var(--mono); color: var(--ink); }
.score-line { font-size: 28px; margin: 0 0 8px; }
.score-line__n { font-size: 72px; font-weight: 700; line-height: 1; }
.result-list { padding-left: 1.4em; }
.result-list .is-right::marker { color: var(--gold); }
.result-list .is-wrong { color: var(--ink-2); }

/* ---- footer ------------------------------------------------------------------------------------- */
.site-footer { border-top: 1px solid var(--ink); margin-top: 40px; background: var(--paper); }
.site-footer__in { max-width: 1240px; margin: 0 auto; padding: 20px var(--gutter) 32px; display: flex; flex-wrap: wrap; justify-content: space-between; gap: 8px 24px; font-size: 15px; color: var(--ink-2); }
.site-footer p { margin: 0; }
/* The facade's herringbone, used once as a texture band. */
.herringbone { height: 28px; background-color: var(--ink);
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='28' height='28' viewBox='0 0 28 28'%3E%3Cpath d='M0 14 L14 0 L14 7 L7 14 Z M14 28 L28 14 L28 21 L21 28 Z' fill='%23B8913A'/%3E%3Cpath d='M14 0 L28 14 L21 14 L14 7 Z M0 14 L14 28 L7 28 L0 21 Z' fill='%23474747'/%3E%3C/svg%3E");
  background-size: 28px 28px; }