:root {
  color-scheme: light;

  --bg: #ffffff;
  --bg-elev: #ffffff;
  --bg-mute: #f3f5f8;
  --ink: #000000;
  --ink-2: #1c1c1c;
  --mute: #5a6573;
  --line: #e4e8ee;
  --line-strong: #c9d1dc;
  --accent: #1d4ed8;
  --accent-2: #1e3a8a;
  --accent-soft: rgba(29, 78, 216, 0.08);
  --accent-ink: #fff;
  --ok: #0f766e;
  --ok-soft: rgba(15, 118, 110, 0.1);
  --warn: #0e7490;
  --warn-soft: rgba(14, 116, 144, 0.1);
  --code-bg: #0b1220;
  --code-ink: #e8eef6;
  --code-mute: #8b97a8;
  --shadow: 0 20px 50px rgba(15, 23, 42, 0.06);
  --radius: 14px;
  --wrap: 1120px;
  --prose: 40rem;
  --font: "IBM Plex Sans", system-ui, sans-serif;
  --serif: "Instrument Serif", "Iowan Old Style", Georgia, serif;
  --mono: "IBM Plex Mono", ui-monospace, monospace;
  --ease: cubic-bezier(0.22, 1, 0.36, 1);
}

[data-theme="dark"] {
  color-scheme: dark;
  --bg: #070b12;
  --bg-elev: #0e1520;
  --bg-mute: #151d2a;
  --ink: #f4f7fb;
  --ink-2: #c5ced8;
  --mute: #8b97a8;
  --line: #1e293b;
  --line-strong: #334155;
  --accent: #93c5fd;
  --accent-2: #bfdbfe;
  --accent-soft: rgba(147, 197, 253, 0.12);
  --accent-ink: #070b12;
  --ok: #5eead4;
  --ok-soft: rgba(94, 234, 212, 0.12);
  --warn: #67e8f9;
  --warn-soft: rgba(103, 232, 249, 0.12);
  --code-bg: #05080e;
  --code-ink: #e8eef6;
  --code-mute: #8b97a8;
  --shadow: 0 24px 60px rgba(0, 0, 0, 0.4);
}

*,
*::before,
*::after { box-sizing: border-box; }

html { scroll-behavior: smooth; font-size: 19px; }

html, body { margin: 0; min-height: 100%; }

body {
  font-family: var(--font);
  font-size: 1.1rem;
  line-height: 1.65;
  color: var(--ink);
  background:
    radial-gradient(1200px 500px at 80% -10%, var(--accent-soft), transparent 55%),
    var(--bg);
  letter-spacing: -0.011em;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 0.18em; }
a:hover { color: var(--accent-2); }

img, svg { max-width: 100%; display: block; }
button, input { font: inherit; color: inherit; }
button { cursor: pointer; background: none; border: 0; padding: 0; }

code, kbd {
  font-family: var(--mono);
  font-size: 0.86em;
}

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
}

.skip {
  position: absolute;
  left: 1rem;
  top: -4rem;
  background: var(--ink);
  color: var(--bg);
  padding: 0.5rem 0.8rem;
  z-index: 80;
}
.skip:focus { top: 0.8rem; }

.wrap {
  width: min(var(--wrap), calc(100% - 2.5rem));
  margin-inline: auto;
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  backdrop-filter: blur(18px) saturate(1.2);
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  border-bottom: 1px solid var(--line);
}

.bar {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  min-height: 72px;
}

.logo {
  font-family: var(--mono);
  font-weight: 500;
  font-size: 1.2rem;
  letter-spacing: -0.06em;
  color: var(--ink);
  text-decoration: none;
  display: flex;
  align-items: baseline;
  gap: 0.05em;
}
.logo:hover { color: var(--ink); }
.logo span { color: var(--accent); }

.nav {
  display: flex;
  gap: 0.15rem;
  margin-right: auto;
}
.nav a {
  color: var(--ink-2);
  text-decoration: none;
  padding: 0.4rem 0.7rem;
  border-radius: 8px;
  font-size: 1.08rem;
}
.nav a:hover,
.nav a[aria-current="page"] {
  color: var(--ink);
  background: var(--accent-soft);
}

.bar-actions {
  display: flex;
  align-items: center;
  gap: 0.3rem;
  margin-left: auto;
}

.icon-btn,
.menu {
  width: 38px;
  height: 38px;
  display: grid;
  place-items: center;
  border-radius: 10px;
  color: var(--ink-2);
}
.icon-btn:hover,
.menu:hover { background: var(--bg-mute); color: var(--ink); }
.menu { display: none; }

.kbd-hint {
  display: none;
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--mute);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 0.12rem 0.4rem;
  margin-right: 0.2rem;
}
@media (min-width: 900px) { .kbd-hint { display: inline; } }

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  height: 52px;
  padding: 0 1.3rem;
  font-size: 1.05rem;
  border-radius: 10px;
  font-weight: 500;
  text-decoration: none;
  transition: transform 0.25s var(--ease), background 0.2s, color 0.2s;
}
.btn:hover { transform: translateY(-1px); }
.btn-primary {
  background: var(--ink);
  color: var(--bg);
}
.btn-primary:hover { background: var(--ink); color: var(--bg); }
[data-theme="dark"] .btn-primary {
  background: var(--accent);
  color: var(--accent-ink);
}
.btn-ghost {
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--line-strong);
}
.btn-ghost:hover { background: var(--bg-elev); color: var(--ink); }

/* Hero */
.hero {
  padding: clamp(3.2rem, 8vw, 6.5rem) 0 3.5rem;
}
.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: clamp(2rem, 5vw, 4.5rem);
  align-items: center;
}
.kicker {
  font-family: var(--mono);
  font-size: 0.78rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--mute);
  margin: 0 0 1rem;
}
.hero h1 {
  font-family: var(--serif);
  font-weight: 400;
  font-size: clamp(3.1rem, 7vw, 5.2rem);
  line-height: 1.02;
  letter-spacing: -0.03em;
  margin: 0 0 1.1rem;
}
.lede {
  font-size: 1.32rem;
  color: var(--ink-2);
  max-width: 34rem;
  margin: 0 0 1.8rem;
}
.hero-actions { display: flex; flex-wrap: wrap; gap: 0.7rem; }

.code-card {
  background: var(--code-bg);
  color: var(--code-ink);
  border-radius: 16px;
  padding: 1rem 1.1rem 1.15rem;
  box-shadow: var(--shadow);
  font-family: var(--mono);
  font-size: 0.92rem;
  overflow: hidden;
}
.code-card .dots {
  display: flex;
  gap: 0.35rem;
  margin-bottom: 0.9rem;
}
.code-card .dots i {
  width: 8px; height: 8px; border-radius: 50%;
  background: #243044;
  display: block;
}
.code-card .dots i:nth-child(1) { background: #ff5f57; }
.code-card .dots i:nth-child(2) { background: #febc2e; }
.code-card .dots i:nth-child(3) { background: #28c840; }
.code-card .c-mute { color: var(--code-mute); }
.code-card .c-key { color: #8ea0ff; }
.code-card .c-str { color: #9ddeb0; }
.code-card .c-fn { color: #7dd3fc; }
.code-card pre { margin: 0; white-space: pre-wrap; }

/* Sections */
.section { padding: 1.2rem 0 4.2rem; }
.section-head {
  display: flex;
  justify-content: space-between;
  align-items: end;
  gap: 1rem;
  margin-bottom: 1.5rem;
}
.section-head h2 {
  font-family: var(--serif);
    font-size: clamp(2.05rem, 3.2vw, 2.6rem);
  font-weight: 400;
  letter-spacing: -0.03em;
  margin: 0;
}
.section-head p { margin: 0.35rem 0 0; color: var(--mute); }
.more { font-size: 1.02rem; white-space: nowrap; }

.formats {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
}
.format {
  display: block;
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.35rem 1.3rem 1.4rem;
  text-decoration: none;
  color: inherit;
  min-height: 100%;
  transition: border-color 0.2s, transform 0.25s var(--ease);
}
.format:hover {
  border-color: var(--ink);
  transform: translateY(-2px);
  color: inherit;
}
.format .n {
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--accent);
  margin-bottom: 1.4rem;
}
.format h3 {
  font-size: 1.38rem;
  margin: 0 0 0.4rem;
  letter-spacing: -0.03em;
}
.format p { margin: 0; color: var(--mute); font-size: 1.05rem; }

.tracks {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr;
  gap: 1rem;
}
.track {
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.3rem;
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
  min-height: 220px;
  transition: border-color 0.2s, transform 0.25s var(--ease);
}
.track:hover { border-color: var(--ink); transform: translateY(-2px); color: inherit; }
.track.featured {
  background: var(--ink);
  color: var(--bg);
  border-color: var(--ink);
}
.track.featured:hover { color: var(--bg); }
.track.featured p { color: color-mix(in srgb, var(--bg) 72%, transparent); }
.track .meta {
  font-family: var(--mono);
  font-size: 0.75rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--mute);
  margin-bottom: auto;
}
.track.featured .meta { color: color-mix(in srgb, var(--bg) 62%, transparent); }
.track h3 {
  font-size: 1.5rem;
  letter-spacing: -0.03em;
  margin: 1.2rem 0 0.4rem;
}
.track p { margin: 0; color: var(--mute); font-size: 1.05rem; }

.topics {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.75rem;
}
.topic {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  padding: 1rem 1.05rem;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--bg-elev);
  text-decoration: none;
  color: inherit;
}
.topic:hover { border-color: var(--ink); color: inherit; }
.topic strong { letter-spacing: -0.02em; font-size: 1.08rem; }
.topic span { color: var(--mute); font-size: 0.95rem; }

.path {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--bg-elev);
}
.path-step {
  padding: 1.2rem 1.15rem 1.3rem;
  border-right: 1px solid var(--line);
  text-decoration: none;
  color: inherit;
}
.path-step:last-child { border-right: 0; }
.path-step:hover { background: var(--accent-soft); color: inherit; }
.path-step .n {
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--accent);
}
.path-step h3 { margin: 0.55rem 0 0.25rem; font-size: 1.15rem; letter-spacing: -0.02em; }
.path-step p { margin: 0; color: var(--mute); font-size: 1rem; }

/* Page headers */
.page-hero {
  padding: 2.6rem 0 1.6rem;
  border-bottom: 1px solid var(--line);
  margin-bottom: 2rem;
}
.page-hero h1 {
  font-family: var(--serif);
  font-weight: 400;
  font-size: clamp(2.5rem, 5.2vw, 3.8rem);
  letter-spacing: -0.03em;
  line-height: 1.08;
  margin: 0 0 0.7rem;
}
.page-hero p { margin: 0; max-width: 40rem; color: var(--ink-2); font-size: 1.22rem; }

.crumbs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  font-size: 0.92rem;
}
.crumbs ol {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.15rem 0.4rem;
  align-items: center;
}
.crumbs li { display: inline; }
.crumbs-sep { opacity: 0.5; }
.crumbs a { color: var(--mute); text-decoration: none; }
.crumbs a:hover { color: var(--ink); }
.crumbs span[aria-hidden] { opacity: 0.5; }

/* Catalog cards */
.catalog {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1rem;
  padding-bottom: 4rem;
}
.card {
  display: block;
  padding: 1.35rem 1.4rem 1.45rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--bg-elev);
  text-decoration: none;
  color: inherit;
  transition: border-color 0.2s, transform 0.25s var(--ease);
}
.card:hover { border-color: var(--ink); transform: translateY(-2px); color: inherit; }
.card .meta {
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--mute);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.card h2 {
  font-size: 1.5rem;
  letter-spacing: -0.03em;
  margin: 0.7rem 0 0.4rem;
}
.card p { margin: 0; color: var(--mute); }

.list {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--bg-elev);
  margin-bottom: 3.5rem;
}
.list a {
  display: grid;
  grid-template-columns: 3.2rem 1fr auto;
  gap: 0.8rem;
  align-items: center;
  padding: 0.95rem 1.15rem;
  text-decoration: none;
  color: inherit;
  border-bottom: 1px solid var(--line);
}
.list a:last-child { border-bottom: 0; }
.list a:hover { background: var(--accent-soft); color: inherit; }
.list .n {
  font-family: var(--mono);
  font-size: 0.8rem;
  color: var(--mute);
}
.list h3 { margin: 0; font-size: 1.18rem; font-weight: 500; letter-spacing: -0.02em; }
.list .hint { color: var(--mute); font-size: 0.95rem; }

/* Lesson layout */
.lesson {
  display: grid;
  grid-template-columns: 230px minmax(0, 1fr);
  gap: 3rem;
  padding-bottom: 5rem;
  align-items: start;
}
.toc {
  position: sticky;
  top: 88px;
  font-size: 1rem;
}
.toc-title,
.toc h4 {
  margin: 0 0 0.7rem;
  font-size: 0.75rem;
  font-family: var(--mono);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--mute);
  font-weight: 500;
}
.toc a {
  display: block;
  color: var(--ink-2);
  text-decoration: none;
  padding: 0.28rem 0;
  border-left: 2px solid var(--line);
  padding-left: 0.75rem;
}
.toc a:hover,
.toc a[aria-current="page"] {
  color: var(--ink);
  border-color: var(--accent);
}

.prose { max-width: var(--prose); }
.prose h1 {
  font-family: var(--serif);
  font-weight: 400;
  font-size: clamp(2.25rem, 4.4vw, 3.1rem);
  letter-spacing: -0.03em;
  line-height: 1.12;
  margin: 0 0 0.8rem;
}
.prose .lead {
  font-size: 1.32rem;
  color: var(--ink-2);
  margin: 0 0 1.8rem;
}
.prose h2 {
  font-size: 1.5rem;
  letter-spacing: -0.03em;
  margin: 2.2rem 0 0.7rem;
}
.prose h3 {
  font-size: 1.2rem;
  margin: 1.6rem 0 0.5rem;
}
.prose p { margin: 0 0 1rem; }
.prose p code, .prose li code, .prose .lead code {
  background: var(--bg-mute);
  padding: 0.08rem 0.35rem;
  border-radius: 5px;
  font-size: 0.88em;
}
.prose ul, .prose ol { margin: 0 0 1.1rem; padding-left: 1.2rem; }
.prose li { margin: 0.25rem 0; }
.prose li::marker { color: var(--mute); }
.prose strong { font-weight: 600; }

.note, .warn, .ok {
  border-radius: 12px;
  padding: 0.9rem 1rem;
  margin: 1.2rem 0;
  font-size: 1.02rem;
}
.note { background: var(--accent-soft); }
.warn { background: var(--warn-soft); }
.ok { background: var(--ok-soft); }
.note strong, .warn strong, .ok strong { display: block; margin-bottom: 0.15rem; }

.table-wrap { overflow-x: auto; margin: 1.1rem 0 1.4rem; }
table {
  width: 100%;
  border-collapse: collapse;
  font-size: 1rem;
}
th, td {
  text-align: left;
  padding: 0.55rem 0.7rem;
  border-bottom: 1px solid var(--line);
  vertical-align: top;
}
th { color: var(--mute); font-weight: 500; font-size: 0.8rem; letter-spacing: 0.04em; text-transform: uppercase; }
td code { background: var(--bg-mute); padding: 0.08rem 0.32rem; border-radius: 5px; }

pre.code {
  position: relative;
  background: var(--code-bg);
  color: var(--code-ink);
  border-radius: 10px;
  padding: 1.5rem 1rem 0.65rem;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: 0.92rem;
  line-height: 1.5;
  margin: 0.65rem 0 0.8rem;
}
pre.code code { font-family: inherit; }
pre.code .lang {
  position: absolute;
  top: 0.38rem;
  left: 1rem;
  font-size: 0.64rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--code-mute);
}
.copy {
  position: absolute;
  top: 0.22rem;
  right: 0.4rem;
  color: var(--code-mute);
  font-size: 0.7rem;
  font-family: var(--font);
  padding: 0.18rem 0.45rem;
  border-radius: 6px;
}
.copy:hover { color: var(--code-ink); background: #1e293b; }
.ok pre.code, .note pre.code, .warn pre.code { margin: 0.5rem 0 0.25rem; }

pre.code .tok-kw { color: #569cd6; }
pre.code .tok-ctrl { color: #c586c0; }
pre.code .tok-str { color: #ce9178; }
pre.code .tok-cmt { color: #6a9955; font-style: italic; }
pre.code .tok-num { color: #b5cea8; }
pre.code .tok-fn { color: #dcdcaa; }
pre.code .tok-type { color: #4ec9b0; }
pre.code .tok-tag { color: #569cd6; }
pre.code .tok-attr { color: #9cdcfe; }
pre.code .tok-bool { color: #569cd6; }
.list a.is-done .n { color: var(--ok); }
[data-complete].is-done {
  border-color: var(--ok);
  color: var(--ok);
}

.pager {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2.6rem;
  padding-top: 1.4rem;
  border-top: 1px solid var(--line);
}
.pager a {
  text-decoration: none;
  color: inherit;
  max-width: 48%;
}
.pager a:hover { color: var(--accent); }
.pager small { display: block; color: var(--mute); font-size: 0.78rem; }

mark.done {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.84rem;
  color: var(--ok);
  margin: 0 0 0.8rem;
}

/* Search */
.search {
  position: fixed;
  inset: 0;
  z-index: 70;
  background: rgba(7, 11, 18, 0.45);
  display: grid;
  place-items: start center;
  padding: 12vh 1rem 2rem;
}
.search[hidden] { display: none; }
.search-panel {
  width: min(640px, 100%);
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: 16px;
  box-shadow: var(--shadow);
  overflow: hidden;
}
.search-panel input {
  width: 100%;
  border: 0;
  background: transparent;
  padding: 1rem 1.15rem;
  outline: none;
  border-bottom: 1px solid var(--line);
  font-size: 18px;
}
.search-list { list-style: none; margin: 0; padding: 0.4rem; max-height: 50vh; overflow: auto; }
.search-list a {
  display: block;
  padding: 0.7rem 0.8rem;
  border-radius: 10px;
  text-decoration: none;
  color: inherit;
}
.search-list a:hover,
.search-list a.active { background: var(--accent-soft); }
.search-list small { display: block; color: var(--mute); }
.search-empty { padding: 1.2rem; color: var(--mute); }

.feedback {
  position: fixed;
  inset: 0;
  z-index: 72;
  background: rgba(7, 11, 18, 0.45);
  display: grid;
  place-items: start center;
  padding: 12vh 1rem 2rem;
}
.feedback[hidden] { display: none; }
.feedback-panel {
  position: relative;
  width: min(480px, 100%);
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: 16px;
  box-shadow: var(--shadow);
  padding: 1.35rem 1.3rem 1.4rem;
}
.feedback-panel h2 {
  margin: 0 2rem 1rem 0;
  font-size: 1.35rem;
  letter-spacing: -0.03em;
}
.feedback-close {
  position: absolute;
  top: 0.7rem;
  right: 0.7rem;
  width: 36px;
  height: 36px;
  border: 0;
  background: transparent;
  color: var(--mute);
  font-size: 1.4rem;
  line-height: 1;
  cursor: pointer;
  border-radius: 8px;
}
.feedback-close:hover { color: var(--ink); background: var(--accent-soft); }
.feedback-panel label {
  display: block;
  font-size: 0.92rem;
  font-weight: 500;
  margin: 0 0 0.35rem;
  color: var(--ink);
}
.feedback-panel input[type="text"],
.feedback-panel textarea {
  width: 100%;
  margin: 0 0 0.9rem;
  padding: 0.7rem 0.8rem;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--bg);
  color: var(--ink);
  font: inherit;
  font-size: 1rem;
}
.feedback-panel textarea { min-height: 8.5rem; resize: vertical; }
.feedback-panel input:focus,
.feedback-panel textarea:focus {
  outline: none;
  border-color: var(--accent);
}
.feedback-panel .hp {
  position: absolute;
  left: -9999px;
  width: 1px;
  height: 1px;
  overflow: hidden;
}
.feedback-status {
  margin: 0 0 0.8rem;
  font-size: 0.95rem;
}
.feedback-status.is-ok { color: var(--ok); }
.feedback-status.is-err { color: #b45309; }
.feedback-panel .btn { width: 100%; border: 0; cursor: pointer; }
.feedback-panel .btn[disabled] { opacity: 0.6; cursor: wait; }

/* Footer */
.site-footer {
  border-top: 1px solid var(--line);
  padding: 2.4rem 0 2.6rem;
  color: var(--mute);
  font-size: 1.02rem;
}
.foot {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr 1fr;
  gap: 1.5rem;
}
.foot strong { display: block; color: var(--ink); margin-bottom: 0.55rem; font-weight: 600; }
.foot a { display: block; color: var(--mute); text-decoration: none; padding: 0.18rem 0; }
.foot a:hover { color: var(--ink); }
.foot .foot-feedback {
  display: block;
  width: 100%;
  margin: 0;
  padding: 0.18rem 0;
  border: 0;
  background: none;
  color: var(--mute);
  font: inherit;
  text-align: left;
  cursor: pointer;
}
.foot .foot-feedback:hover { color: var(--ink); }
.foot .brand {
  font-family: var(--mono);
  color: var(--ink);
  font-size: 1.05rem;
  margin-bottom: 0.4rem;
}
.copyline { margin-top: 2rem; font-size: 0.82rem; }

/* 404 */
.notfound {
  min-height: 70vh;
  display: grid;
  place-content: center;
  text-align: center;
  padding: 4rem 1rem;
}
.notfound h1 {
  font-family: var(--serif);
  font-size: clamp(3rem, 8vw, 5rem);
  margin: 0;
  letter-spacing: -0.04em;
}

@media (max-width: 900px) {
  .hero-grid,
  .tracks,
  .path,
  .lesson,
  .foot { grid-template-columns: 1fr; }
  .formats,
  .topics,
  .catalog { grid-template-columns: 1fr 1fr; }
  .path-step { border-right: 0; border-bottom: 1px solid var(--line); }
  .path-step:last-child { border-bottom: 0; }
  .tracks .track { min-height: 0; }
  .nav { display: none; }
  .menu { display: grid; }
  .nav.open {
    display: flex;
    flex-direction: column;
    position: absolute;
    left: 0; right: 0;
    top: 72px;
    background: var(--bg-elev);
    border-bottom: 1px solid var(--line);
    padding: 0.6rem 1.25rem 1rem;
  }
  .toc { position: static; margin-bottom: 1.4rem; }
  .list a { grid-template-columns: 2.4rem 1fr; }
  .list .hint { display: none; }
}

@media (max-width: 620px) {
  .formats,
  .topics,
  .catalog { grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .btn, .format, .track, .card { transition: none; }
}

.lang-wrap { position: relative; }
.lang-btn {
  height: 38px;
  padding: 0 0.65rem;
  border-radius: 10px;
  font-family: var(--mono);
  font-size: 0.78rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--ink-2);
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}
.lang-btn:hover { background: var(--bg-mute); color: var(--ink); }
.lang-panel {
  position: absolute;
  right: 0;
  top: calc(100% + 6px);
  width: min(280px, calc(100vw - 2rem));
  max-height: min(70vh, 420px);
  overflow: auto;
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: 12px;
  box-shadow: var(--shadow);
  padding: 0.4rem;
  z-index: 70;
}
.lang-panel[hidden] { display: none; }
.lang-panel input {
  width: 100%;
  border: 1px solid var(--line);
  background: var(--bg);
  border-radius: 8px;
  padding: 0.45rem 0.6rem;
  margin-bottom: 0.35rem;
  font-size: 16px;
}
.lang-panel a {
  display: block;
  padding: 0.45rem 0.6rem;
  border-radius: 8px;
  text-decoration: none;
  color: var(--ink);
  font-size: 0.92rem;
}
.lang-panel a:hover,
.lang-panel a.is-on { background: var(--accent-soft); }

.lang-suggest {
  position: fixed;
  top: 84px;
  right: 1.15rem;
  z-index: 80;
  width: min(300px, calc(100% - 2rem));
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: 14px;
  box-shadow: var(--shadow);
  padding: 1rem 1.05rem 1.05rem;
}
.lang-suggest p { margin: 0 0 0.85rem; color: var(--ink-2); font-size: 0.95rem; line-height: 1.45; }
.lang-suggest .row { display: flex; gap: 0.5rem; flex-wrap: wrap; }
.lang-suggest .x {
  position: absolute;
  top: 0.45rem;
  right: 0.5rem;
  width: 32px;
  height: 32px;
  border-radius: 8px;
  color: var(--mute);
}
.lang-suggest .x:hover { background: var(--bg-mute); color: var(--ink); }
.lang-suggest .btn { height: 40px; font-size: 0.92rem; padding: 0 0.9rem; }

.topic-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
  margin-bottom: 3.5rem;
}
.topic-grid .card h2 { font-size: 1.22rem; margin: 0.35rem 0 0.25rem; }
.sub-list { margin: 0 0 2rem; padding: 0; list-style: none; }
.sub-list li {
  border-bottom: 1px solid var(--line);
  padding: 0.85rem 0;
}
.sub-list strong { display: block; margin-bottom: 0.2rem; }
.tree h2 {
  font-size: 1.25rem;
  margin: 2rem 0 0.4rem;
  letter-spacing: -0.03em;
}
.tree a {
  display: block;
  padding: 0.7rem 0;
  border-bottom: 1px solid var(--line);
  text-decoration: none;
  color: var(--ink);
}
.tree a:hover { color: var(--accent); }
.tree .src,
.page-hero .src {
  font-size: 0.95rem;
  color: var(--mute);
  margin: 0 0 0.2rem;
}

@media (max-width: 900px) {
  .topic-grid { grid-template-columns: 1fr 1fr; }
  .lang-suggest { top: auto; bottom: 1rem; right: 1rem; left: 1rem; width: auto; }
}
@media (max-width: 620px) {
  .topic-grid { grid-template-columns: 1fr; }
}

/* Textbook content */
.book-group { margin: 0 0 2.4rem; }
.book-group > h2 {
  font-size: 1.35rem;
  letter-spacing: -0.03em;
  margin: 0 0 0.85rem;
}
.chapter { margin: 0 0 2.2rem; }
.chapter > h2 {
  font-size: 1.28rem;
  letter-spacing: -0.03em;
  margin: 0 0 0.7rem;
  scroll-margin-top: 5rem;
}
.letter-index {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin: 0 0 1.8rem;
}
.letter-index a {
  min-width: 2.25rem;
  height: 2.25rem;
  padding: 0 0.4rem;
  display: grid;
  place-items: center;
  border: 1px solid var(--line);
  border-radius: 10px;
  text-decoration: none;
  color: inherit;
  font-weight: 600;
  font-size: 0.95rem;
  background: var(--bg-elev);
}
.letter-index a:hover {
  border-color: var(--accent);
  color: var(--accent);
}
.prose .slang-aka {
  color: var(--mute);
  margin: -0.35rem 0 1rem;
  font-size: 1.05rem;
}
.prose .slang-en {
  color: var(--ink-2);
  font-size: 0.98rem;
  margin: 0 0 1rem;
}
.toc {
  max-height: calc(100vh - 110px);
  overflow: auto;
}
.toc .toc-all {
  margin-top: 0.6rem;
  color: var(--mute);
  font-size: 0.92rem;
}
.prose dfn { font-style: italic; font-weight: 500; }
.prose dl { margin: 0 0 1.4rem; }
.prose dt { margin-top: 1rem; font-weight: 600; }
.prose dd { margin: 0.2rem 0 0 0; color: var(--ink-2); }
.prose img {
  border-radius: 12px;
  border: 1px solid var(--line);
  margin: 1rem 0 1.3rem;
}
.prose iframe.demo {
  width: 100%;
  min-height: 240px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #fff;
  margin: 1rem 0 1.3rem;
}
.filetree {
  list-style: none;
  margin: 0 0 1.1rem;
  padding: 0.8rem 1rem;
  background: var(--bg-mute);
  border-radius: 12px;
  font-family: var(--mono);
  font-size: 0.92rem;
}
.filetree li { padding: 0.12rem 0; }
.refs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin: 0 0 1.2rem;
}
.refs code {
  background: var(--bg-mute);
  padding: 0.12rem 0.4rem;
  border-radius: 6px;
}
.prose .code-label {
  display: block;
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--mute);
  letter-spacing: 0.04em;
  margin: 0.4rem 0 -0.7rem;
}

/* Reference catalog */
body.is-ref {
  --ref-manual: #0f766e;
  --ref-tasker: #c2410c;
  --ref-glossary: #6d28d9;
  --ref-slang: #be185d;
  --ref-projery: #15803d;
  --ref-job: #1d4ed8;
  --ref-other: #475569;
  background:
    radial-gradient(70rem 28rem at 8% -12%, color-mix(in srgb, var(--ref-manual) 14%, transparent), transparent 60%),
    radial-gradient(50rem 22rem at 92% 0%, color-mix(in srgb, var(--accent) 10%, transparent), transparent 58%),
    var(--bg);
}
[data-theme="dark"] body.is-ref {
  --ref-manual: #5eead4;
  --ref-tasker: #fdba74;
  --ref-glossary: #c4b5fd;
  --ref-slang: #f9a8d4;
  --ref-projery: #86efac;
  --ref-job: #93c5fd;
  --ref-other: #94a3b8;
}
body.is-ref .page-hero {
  border-bottom: 0;
  padding: 2.4rem 0 1.8rem;
  margin-bottom: 1.2rem;
}
body.is-ref .page-hero h1 {
  font-family: var(--font);
  font-weight: 600;
  font-size: clamp(2.2rem, 5vw, 3.4rem);
  letter-spacing: -0.055em;
  line-height: 1.05;
}
body.is-ref .ref-lead {
  max-width: 38rem;
  margin: 0 0 1rem;
  color: var(--ink-2);
  font-size: 1.12rem;
}
body.is-ref .ref-stats {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}
body.is-ref .ref-stats span {
  display: inline-flex;
  align-items: center;
  height: 2rem;
  padding: 0 0.8rem;
  border-radius: 999px;
  background: var(--bg-mute);
  border: 1px solid var(--line);
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--ink-2);
}
body.is-ref .list a .n { color: var(--ref-manual); }
.ref-band {
  margin: 0 0 2.6rem;
}
.ref-band-head {
  display: flex;
  align-items: baseline;
  gap: 0.7rem;
  margin: 0 0 1.05rem;
}
.ref-band-head h2 {
  margin: 0;
  font-size: 1.28rem;
  font-weight: 600;
  letter-spacing: -0.04em;
}
.ref-band-n {
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--mute);
}
.ref-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.8rem;
}
.ref-card {
  --ref-tone: var(--ref-other);
  display: flex;
  flex-direction: column;
  gap: 0.7rem;
  min-height: 10.4rem;
  padding: 1.05rem 1.1rem 1.05rem;
  border: 1px solid color-mix(in srgb, var(--ref-tone) 18%, var(--line));
  border-radius: 18px;
  background: var(--bg-elev);
  color: inherit;
  text-decoration: none;
  box-shadow: 0 1px 0 color-mix(in srgb, var(--ink) 4%, transparent);
  transition: transform 0.22s var(--ease), box-shadow 0.22s var(--ease), border-color 0.22s;
}
.ref-card[data-kind="manual"] { --ref-tone: var(--ref-manual); }
.ref-card[data-kind="tasker"] { --ref-tone: var(--ref-tasker); }
.ref-card[data-kind="glossary"] { --ref-tone: var(--ref-glossary); }
.ref-card[data-kind="slang"] { --ref-tone: var(--ref-slang); }
.ref-card[data-kind="projery"] { --ref-tone: var(--ref-projery); }
.ref-card[data-kind="job"] { --ref-tone: var(--ref-job); }
.ref-card:hover {
  transform: translateY(-3px);
  border-color: color-mix(in srgb, var(--ref-tone) 45%, var(--line));
  box-shadow: 0 14px 32px color-mix(in srgb, var(--ref-tone) 14%, transparent);
  color: inherit;
}
.ref-card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.6rem;
}
.ref-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 2.35rem;
  height: 2.35rem;
  padding: 0 0.45rem;
  border-radius: 11px;
  background: color-mix(in srgb, var(--ref-tone) 16%, var(--bg));
  color: var(--ref-tone);
  font-family: var(--mono);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: -0.02em;
}
.ref-kind {
  font-family: var(--mono);
  font-size: 0.68rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--mute);
}
.ref-title {
  display: block;
  font-size: 1.12rem;
  font-weight: 600;
  letter-spacing: -0.035em;
  line-height: 1.28;
}
.ref-meta {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.6rem;
  margin-top: auto;
}
.ref-topic {
  color: var(--mute);
  font-size: 0.88rem;
}
.ref-n {
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--mute);
  white-space: nowrap;
}
@media (max-width: 980px) {
  .ref-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (max-width: 620px) {
  .ref-grid { grid-template-columns: 1fr; }
  .ref-card { min-height: 0; }
}

/* Python course trainer */
.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0);
  border: 0;
}
body.is-course .course-wrap { max-width: 1240px; }
.course-app {
  display: grid;
  grid-template-columns: 240px minmax(0, 1fr);
  gap: 2.2rem;
  padding-bottom: 4rem;
  align-items: start;
}
.course-toc { max-height: calc(100vh - 110px); overflow: auto; }
.course-toc .toc-all { display: inline-block; margin: 0 0 0.8rem; }
.course-toc h4 { margin-top: 0.9rem; }
.course-toc a.is-done { color: var(--ok); }
.course-prose { max-width: none; }
.trainer {
  margin: 1.6rem 0 0;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--bg-elev);
  overflow: hidden;
}
.trainer-head {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.7rem 1rem;
  border-bottom: 1px solid var(--line);
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--mute);
}
#py-editor {
  display: block;
  width: 100%;
  min-height: 14rem;
  margin: 0;
  padding: 1rem 1.05rem;
  border: 0;
  resize: vertical;
  background: var(--code-bg);
  color: var(--code-ink);
  font-family: var(--mono);
  font-size: 0.92rem;
  line-height: 1.55;
  tab-size: 4;
}
#py-editor:focus { outline: none; }
.trainer .CodeMirror {
  height: 16.5rem;
  background: var(--code-bg);
  color: #c5ced8;
  font-family: var(--mono);
  font-size: 0.92rem;
  line-height: 1.6;
}
.trainer .CodeMirror-gutters {
  background: var(--code-bg);
  border-right: 1px solid rgba(148, 163, 184, 0.16);
  color: #6b7685;
}
.trainer .CodeMirror-linenumber { color: #6b7685; }
.trainer .CodeMirror-cursor { border-left: 1.5px solid #c5ced8; }
.trainer .CodeMirror-selected { background: rgba(148, 163, 184, 0.16); }
.trainer .CodeMirror-focused .CodeMirror-selected { background: rgba(148, 163, 184, 0.22); }
.trainer .CodeMirror-activeline-background { background: rgba(148, 163, 184, 0.07); }
.trainer .CodeMirror-matchingbracket {
  color: inherit !important;
  background: rgba(126, 190, 176, 0.18);
  outline: none;
}
.trainer .cm-keyword { color: #9b8ec4; }
.trainer .cm-builtin { color: #7ea2c4; }
.trainer .cm-def { color: #c4b48a; }
.trainer .cm-variable { color: #c5ced8; }
.trainer .cm-variable-2 { color: #8fb4c9; }
.trainer .cm-variable-3 { color: #7ebeb0; }
.trainer .cm-property { color: #8fb4c9; }
.trainer .cm-operator { color: #8b95a3; }
.trainer .cm-number { color: #97b89a; }
.trainer .cm-string,
.trainer .cm-string-2 { color: #c4a090; }
.trainer .cm-comment { color: #7b8494; font-style: italic; }
.trainer .cm-meta { color: #7ea2c4; }
.trainer .cm-atom { color: #8aa3c4; }
.trainer .cm-error { color: #c98a8a; }
.trainer-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.55rem;
  padding: 0.75rem 1rem;
  border-top: 1px solid var(--line);
}
.trainer-hint { margin-left: auto; color: var(--mute); font-size: 0.82rem; }
.trainer-console {
  margin: 0;
  padding: 0.8rem 1rem 1rem;
  min-height: 2.5rem;
  background: var(--bg-mute);
  color: var(--ink-2);
  font-family: var(--mono);
  font-size: 0.85rem;
  white-space: pre-wrap;
}
.trainer-tests {
  list-style: none;
  margin: 0;
  padding: 0 1rem 1rem;
}
.trainer-tests li {
  padding: 0.55rem 0.7rem;
  margin: 0 0 0.4rem;
  border-radius: 10px;
  border: 1px solid var(--line);
}
.trainer-tests li.pass { border-color: var(--ok); background: var(--ok-soft); }
.trainer-tests li.fail { border-color: #b45309; background: rgba(180, 83, 9, 0.08); }
.trainer-tests strong { display: block; }
.trainer-tests em { font-style: normal; font-size: 0.82rem; color: var(--mute); }
.trainer-tests span { display: block; margin-top: 0.25rem; font-size: 0.88rem; color: var(--ink-2); }
.trainer-tests code {
  font-family: var(--mono);
  font-size: 0.82rem;
}
@media (max-width: 860px) {
  .course-app { grid-template-columns: 1fr; }
  .course-toc { position: static; max-height: none; }
  .trainer-hint { margin-left: 0; width: 100%; }
}