:root {
  --paper: #fff;
  --canvas: #f5f7fa;
  --ink: #202936;
  --muted: #536277;
  --line: #dce3ec;
  --blue: #1758a8;
  --pale: #e9f1fb;
  --code: #f4f6f9;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  color: var(--ink);
  background: var(--paper);
  font-size: 16px;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
}
a {
  color: var(--blue);
  text-underline-offset: 3px;
}
a:hover {
  text-decoration-thickness: 2px;
}
button,
a,
summary {
  touch-action: manipulation;
}
:focus-visible {
  outline: 3px solid #5895de;
  outline-offset: 4px;
}
h1,
h2,
h3 {
  line-height: 1.25;
  letter-spacing: -0.025em;
}
h1 {
  font-size: clamp(2rem, 4vw, 2.8rem);
  margin: 0.6em 0;
}
h2 {
  font-size: 1.55rem;
  margin: 2.4em 0 0.8em;
  scroll-margin-top: 30px;
}
h3 {
  font-size: 1.15rem;
}
p,
li {
  line-height: 1.8;
}
p {
  margin: 1em 0;
}
li {
  margin: 0.4em 0;
}
strong {
  font-weight: 650;
}
.site-header {
  min-height: 78px;
  padding: 22px 32px;
  border-bottom: 1px solid var(--line);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 20px;
}
.brand {
  font-size: 1.1rem;
  font-weight: 700;
  text-decoration: none;
  color: var(--ink);
}
.site-header > span {
  color: var(--muted);
  font-size: 0.9rem;
}
.layout {
  display: grid;
  grid-template-columns: 255px minmax(0, 780px) 180px;
  gap: 40px;
  max-width: 1390px;
  margin: 0 auto;
  padding: 32px 28px 64px;
}
aside {
  min-width: 0;
}
.course-menu {
  position: sticky;
  top: 24px;
}
.course-menu summary {
  font-weight: 650;
  cursor: pointer;
  padding: 6px 0;
}
.progress-box {
  margin: 18px 0 20px;
}
.progress-box p {
  font-size: 0.86rem;
  margin: 0 0 7px;
}
.progress-box small {
  color: var(--muted);
  font-size: 0.75rem;
}
progress {
  width: 100%;
  height: 6px;
  border: 0;
  background: var(--line);
  border-radius: 4px;
  appearance: none;
}
progress::-webkit-progress-bar {
  background: var(--line);
  border-radius: 4px;
}
progress::-webkit-progress-value {
  background: var(--blue);
  border-radius: 4px;
}
progress::-moz-progress-bar {
  background: var(--blue);
}
.chapters {
  padding: 0;
  margin: 0;
  list-style: none;
}
.chapters li {
  margin: 3px 0;
  line-height: 1.4;
}
.chapters a {
  display: grid;
  grid-template-columns: 20px 1fr 15px;
  gap: 7px;
  padding: 10px 9px;
  border-radius: 5px;
  text-decoration: none;
  color: var(--muted);
  font-size: 0.86rem;
}
.chapters a:hover {
  background: var(--canvas);
}
.chapters a[aria-current='page'] {
  background: var(--pale);
  color: var(--blue);
  font-weight: 600;
}
.chapter-number {
  font-variant-numeric: tabular-nums;
}
.check {
  color: #246641;
}
.chapters .is-done .check::after {
  content: '✓';
}
main {
  min-width: 0;
  outline: none;
}
article {
  font-size: 1.03rem;
}
article > h1 {
  margin-bottom: 1em;
}
article > p:first-of-type {
  color: var(--muted);
  font-size: 1.08rem;
}
pre {
  background: var(--code);
  border: 1px solid var(--line);
  border-radius: 7px;
  padding: 20px;
  overflow: auto;
  line-height: 1.65;
  font-size: 0.85rem;
  tab-size: 2;
}
code {
  font-family: 'SFMono-Regular', Consolas, 'Liberation Mono', monospace;
  font-size: 0.88em;
}
pre code {
  font-size: inherit;
  background: none;
  padding: 0;
}
p code,
li code,
td code {
  background: var(--code);
  padding: 2px 5px;
  border-radius: 3px;
  overflow-wrap: anywhere;
}
blockquote {
  margin: 24px 0;
  border-left: 3px solid #90b4dd;
  padding: 3px 20px;
  color: var(--muted);
  background: #f7faff;
}
blockquote p {
  margin: 10px 0;
}
table {
  display: block;
  overflow: auto;
  border-collapse: collapse;
  width: 100%;
  font-size: 0.9rem;
}
th,
td {
  text-align: left;
  border-bottom: 1px solid var(--line);
  padding: 12px;
  min-width: 135px;
  vertical-align: top;
}
th {
  background: var(--canvas);
}
.pager {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 60px minmax(0, 1fr);
  gap: 15px;
  padding: 15px 0 22px;
  border-bottom: 1px solid var(--line);
  align-items: start;
}
.pager a {
  text-decoration: none;
  min-width: 0;
}
.pager span:not(.page-count) {
  font-weight: 600;
}
.pager small {
  display: block;
  color: var(--muted);
  font-size: 0.76rem;
  margin-top: 6px;
  line-height: 1.4;
}
.pager [data-next] {
  text-align: right;
}
.page-count {
  text-align: center;
  color: var(--muted);
  font-size: 0.82rem;
  padding-top: 3px;
}
.lesson-meta {
  margin-top: 26px;
  display: flex;
  justify-content: space-between;
  color: var(--muted);
  font-size: 0.8rem;
}
.lesson-meta a {
  text-decoration: none;
}
.spoiler-heading {
  margin-top: 38px;
  padding: 14px 16px;
  background: #edf4fb;
  border-left: 3px solid var(--blue);
  border-radius: 0 4px 4px 0;
}
.completion {
  border-top: 1px solid var(--line);
  padding: 28px 0;
  display: flex;
  gap: 15px;
  align-items: center;
  flex-wrap: wrap;
  margin-top: 40px;
}
button,
.primary-link {
  font: inherit;
  cursor: pointer;
  background: var(--blue);
  color: white;
  border: 0;
  border-radius: 5px;
  padding: 12px 18px;
  text-decoration: none;
  display: inline-block;
}
button[aria-pressed='true'] {
  background: #eaf3ee;
  color: #24533c;
}
.completion span {
  font-size: 0.85rem;
  color: var(--muted);
}
.intro .context {
  color: var(--muted);
  font-size: 0.85rem;
  margin-top: 6px;
}
.intro h1 {
  font-size: clamp(2.1rem, 4vw, 2.8rem);
  margin: 0 0 18px;
  line-height: 1.13;
  letter-spacing: -0.04em;
}
.lead {
  font-size: 1.1rem;
  line-height: 1.6;
  margin: 0 0 16px;
  color: var(--muted);
}
.resume-note {
  font-size: 0.85rem;
  color: var(--muted);
}
.primary-link {
  margin: 10px 0;
}
.overview ol {
  list-style: none;
  margin: 0;
  padding: 0;
}
.overview li {
  margin: 0;
}
.overview a {
  display: grid;
  grid-template-columns: 32px 1fr 20px;
  gap: 16px;
  padding: 17px 0;
  border-bottom: 1px solid var(--line);
  text-decoration: none;
  align-items: center;
}
.overview a > span:first-child {
  font-size: 0.8rem;
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}
.overview strong {
  color: var(--ink);
}
.overview a:hover strong {
  color: var(--blue);
}
.about {
  margin-top: 40px;
}
.site-footer {
  border-top: 1px solid var(--line);
  padding: 24px 32px;
  color: var(--muted);
  font-size: 0.8rem;
}
.skip {
  position: absolute;
  left: 10px;
  top: -100px;
  z-index: 10;
  background: white;
  padding: 12px;
}
.skip:focus {
  top: 10px;
}
.storage-note {
  color: #8c391b;
}
@media (max-width: 1199px) {
  .layout {
    grid-template-columns: 225px minmax(0, 1fr);
    gap: 30px;
    max-width: 1100px;
  }
}
@media (max-width: 760px) {
  .site-header {
    padding: 17px 20px;
  }
  .site-header > span {
    display: none;
  }
  .layout {
    display: block;
    padding: 18px 20px 40px;
  }
  .course-menu {
    position: static;
    border: 1px solid var(--line);
    padding: 12px 14px;
    border-radius: 6px;
    margin-bottom: 24px;
  }
  .chapters a {
    padding: 11px 4px;
  }
  .pager {
    gap: 8px;
  }
  .pager small {
    font-size: 0.72rem;
  }
  h1 {
    font-size: 2rem;
  }
  article {
    font-size: 1rem;
  }
  pre {
    padding: 14px;
    font-size: 0.78rem;
    margin-left: 0;
    margin-right: 0;
  }
  .site-footer {
    padding: 20px;
  }
  h2 {
    font-size: 1.35rem;
  }
  .intro h1 {
    font-size: 2.5rem;
  }
}
@media print {
  aside,
  .section-nav,
  .pager,
  .completion,
  .site-header,
  .site-footer,
  .lesson-meta,
  .skip {
    display: none !important;
  }
  .layout {
    display: block;
    padding: 0;
  }
  pre {
    white-space: pre-wrap;
    overflow: visible;
  }
  body {
    font-size: 11pt;
  }
  a {
    color: inherit;
  }
  h2,
  h3 {
    break-after: avoid;
  }
  pre,
  blockquote {
    break-inside: avoid;
  }
}
.search-label {
  display: block;
  font-size: 0.78rem;
  color: var(--muted);
  margin: 16px 0 6px;
}
#chapter-search {
  width: 100%;
  font: inherit;
  font-size: 0.85rem;
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: 9px;
  background: white;
  color: var(--ink);
}
.course-menu {
  max-height: calc(100dvh - var(--menu-reserve, 180px));
  overflow-y: auto;
  overscroll-behavior-y: contain;
  scrollbar-gutter: stable;
  scroll-padding-block: 12px 48px;
  padding-right: 6px;
  padding-bottom: 48px;
}
.tracks {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
}
.track {
  border-top: 2px solid var(--line);
  padding-top: 5px;
}
.track h3 {
  font-size: 1.1rem;
}
.track p {
  font-size: 0.9rem;
  color: var(--muted);
}
.route-label {
  font-size: 0.85rem;
  color: var(--blue);
}
.chapters [hidden] {
  display: none;
}
.site-header > span {
  max-width: 340px;
  text-align: right;
}
.overview [hidden] {
  display: none;
}
@media (max-width: 760px) {
  .course-menu {
    max-height: none;
    overflow: visible;
    padding-bottom: 12px;
  }
  .tracks {
    grid-template-columns: 1fr;
    gap: 12px;
  }
}
.domain-picker {
  border-top: 1px solid var(--line);
  margin-top: 36px;
}

fieldset {
  border: 0;
  border-top: 1px solid var(--line);
  padding: 20px 0;
  margin: 20px 0;
  min-width: 0;
}
legend {
  font-weight: 650;
  padding-right: 12px;
}
.answer-option {
  display: block;
  padding: 8px 4px;
  cursor: pointer;
}
.answer-option input {
  margin-right: 8px;
}
#diagnostic summary {
  cursor: pointer;
  color: var(--blue);
  padding: 16px 0;
}
#diagnostic button {
  padding: 12px 16px;
  margin: 8px 8px 8px 0;
  font: inherit;
  background: var(--blue);
  color: white;
  border: 1px solid var(--blue);
  border-radius: 5px;
  cursor: pointer;
}
#diagnostic .secondary-button {
  background: white;
  color: var(--blue);
}
.gap-result {
  border-left: 3px solid var(--blue);
  padding-left: 20px;
  margin: 24px 0;
}
.gap-result h4 {
  margin-bottom: 4px;
}
#diagnostic-results {
  scroll-margin-top: 24px;
}
[data-domain][hidden],
[hidden] {
  display: none !important;
}
.diagnostic-link {
  display: inline-block;
  padding: 12px 0;
  margin: 0 16px;
}
/* One consistent reader: global controls, full-text results and visible section links. */
.layout {
  grid-template-columns: 255px minmax(0, 820px);
  max-width: 1200px;
}
.header-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  align-items: center;
}
.header-controls label {
  display: flex;
  flex-direction: column;
  font-size: 0.75rem;
  color: var(--muted);
  gap: 4px;
}
.header-controls select {
  min-height: 38px;
  font: inherit;
  font-size: 0.9rem;
  padding: 6px 10px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: white;
  color: var(--ink);
  max-width: 240px;
}
.header-controls a {
  font-size: 0.85rem;
}
.primary-nav {
  display: grid;
  gap: 10px;
  margin: 20px 0;
  font-size: 0.85rem;
}
.domain-vocabulary {
  padding: 14px 18px;
  background: var(--canvas);
  border-left: 3px solid var(--blue);
  margin: 20px 0;
}
.domain-vocabulary p {
  margin: 6px 0;
  font-size: 0.9rem;
}
.domain-vocabulary small {
  color: var(--muted);
  display: block;
  line-height: 1.6;
}
.section-nav {
  margin: 20px 0;
  font-size: 0.9rem;
  display: grid;
  gap: 8px;
  padding: 16px 0;
}
.solution summary {
  cursor: pointer;
  color: var(--blue);
}
.solution {
  margin: 24px 0;
  border: 1px solid var(--line);
  border-radius: 5px;
}
.solution summary {
  padding: 16px;
  font-weight: 650;
}
.solution .answer {
  padding: 0 16px 16px;
}
.search-result {
  margin: 18px 0;
}
.search-result a {
  display: block;
  font-size: 0.85rem;
}
.search-result small {
  display: block;
  color: var(--muted);
  line-height: 1.5;
  overflow-wrap: anywhere;
  margin-top: 5px;
}
#search-results {
  padding: 8px 0;
  border-bottom: 1px solid var(--line);
}
#search-results > p {
  font-size: 0.8rem;
}
.entry-actions {
  display: flex;
  align-items: center;
  gap: 20px;
  flex-wrap: wrap;
}
.entry-actions .primary-link {
  margin: 0;
}
#topics > h2 {
  margin-top: 36px;
}
.topic-groups {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 24px 32px;
  margin-top: 24px;
}
.topic-group {
  border-top: 1px solid var(--line);
  padding-top: 16px;
}
.topic-group h3 {
  margin: 0;
}
.topic-group p {
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.6;
  margin: 10px 0;
}
.topic-group ul {
  list-style: none;
  margin: 0;
  padding: 0;
}
.topic-group li {
  margin: 0;
}
.topic-group a {
  display: inline-block;
  padding: 6px 0;
  line-height: 1.5;
}
#topics,
#practice-entry,
#routes {
  scroll-margin-top: 24px;
}
#scope table {
  width: 100%;
}
#scope td {
  vertical-align: top;
}
.practice-prerequisites {
  margin-bottom: 24px;
}
.code-block {
  margin: 1em 0;
}
.code-tools {
  display: flex;
  justify-content: flex-end;
  align-items: center;
  gap: 12px;
  margin-bottom: 6px;
}
.code-tools [role='status'] {
  color: var(--muted);
  font-size: 0.8rem;
  line-height: 1.4;
}
.copy-code {
  flex-shrink: 0;
  padding: 7px 10px;
  font-size: 0.8rem;
  background: var(--paper);
  color: var(--blue);
  border: 1px solid var(--line);
}
.copy-code:hover {
  background: var(--pale);
}
.code-block pre {
  margin: 0;
}
@media print {
  .code-tools {
    display: none;
  }
}
@media (max-width: 760px) {
  .site-header {
    display: block;
    padding: 18px;
  }
  .header-controls {
    margin-top: 16px;
    display: grid;
    grid-template-columns: minmax(0, 1fr) 96px auto;
    gap: 10px;
  }
  .header-controls label {
    min-width: 0;
  }
  .header-controls select {
    width: 100%;
    min-width: 0;
    min-height: 44px;
    max-width: none;
  }
  .header-controls > a {
    align-self: end;
    padding: 12px 0;
  }
  .layout {
    display: block;
    padding: 20px 18px 48px;
  }
  .topic-groups {
    grid-template-columns: 1fr;
    gap: 24px;
  }
  .entry-actions {
    gap: 12px 20px;
  }
  .intro h1 {
    font-size: 2.1rem;
  }
  .domain-vocabulary {
    padding: 12px;
  }
  .solution .answer {
    padding: 0 12px 12px;
  }
}