/* Lesson page */
.lesson-layout {
    display: grid;
    grid-template-columns: minmax(220px, 250px) minmax(0, 840px);
    justify-content: center;
    gap: clamp(34px, 5vw, 58px);
    width: min(var(--page-width), calc(100% - 72px));
    margin-inline: auto;
    padding: 44px 0 104px;
}

.lesson-toc {
    position: sticky;
    top: 104px;
    align-self: start;
    max-height: calc(100dvh - 130px);
    overflow: auto;
    padding-right: 18px;
}

.lesson-toc h2 {
    margin: 13px 0 22px;
    color: var(--ink);
    font-size: 20px;
    line-height: 1.25;
}

.lesson-toc nav {
    display: grid;
    border-left: 1px solid var(--line);
}

.lesson-toc nav a {
    padding: 8px 0 8px 16px;
    color: var(--muted);
    font-size: 12px;
}

.lesson-toc nav a:hover {
    color: var(--accent);
}

.lesson-toc nav a.active {
    color: var(--accent);
    font-weight: 760;
}

.lesson-progress-box {
    margin-top: 28px;
    padding: 15px;
}

.lesson-progress-box > span {
    display: block;
    margin-bottom: 10px;
    color: var(--muted);
    font-size: 10px;
}

.lesson-progress-box .button {
    width: 100%;
    font-size: 11px;
}

.lesson-article {
    min-width: 0;
}

.lesson-hero {
    padding: 10px 0 38px;
    border-bottom: 1px solid var(--line);
}

.lesson-breadcrumb {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 8px;
    color: var(--muted);
    font-size: 11px;
}

.lesson-breadcrumb a {
    color: var(--accent);
}

.lesson-hero h1 {
    max-width: 780px;
    margin: 24px 0 16px;
    color: var(--ink);
    font-family: var(--serif);
    font-size: clamp(40px, 4.4vw, 64px);
    font-weight: 400;
    line-height: .98;
    letter-spacing: 0;
    text-wrap: balance;
}

.lesson-hero > p {
    max-width: 700px;
    margin: 0;
    color: var(--muted);
    font-size: 15px;
    line-height: 1.75;
}

.lesson-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-top: 26px;
}

.lesson-meta span {
    padding: 7px 10px;
    border: 1px solid var(--line);
    border-radius: 999px;
    background: var(--surface);
    color: var(--muted);
    font-size: 11px;
}

.lesson-section {
    padding: 44px 0;
    border-bottom: 1px solid var(--line);
}

.lesson-section h2 {
    margin: 12px 0 24px;
    color: var(--ink);
    font-size: 32px;
}

.lesson-section p {
    color: color-mix(in srgb, var(--text) 90%, var(--muted));
    font-size: 15px;
    line-height: 1.9;
}

.lesson-section p.lead {
    color: var(--ink);
    font-size: 18px;
    line-height: 1.75;
}

.lesson-section .section-intro {
    max-width: 650px;
    color: var(--muted);
    font-size: 13px;
}

.lesson-section code:not(pre code) {
    padding: .12em .35em;
    border-radius: 6px;
    background: var(--surface-3);
    color: #9b3c43;
    font-family: var(--mono);
    font-size: .9em;
}

.lesson-quick {
    padding-top: 34px;
}

.quick-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 12px;
}

.quick-grid article {
    min-height: 144px;
    padding: 18px;
    border: 1px solid var(--line);
    border-radius: var(--radius-sm);
    background: var(--surface-2);
}

.quick-grid strong {
    display: block;
    color: var(--ink);
    font-size: 14px;
}

.quick-grid p {
    margin: 12px 0 0;
    color: var(--muted);
    font-size: 13px;
    line-height: 1.7;
}

.concept-flow {
    display: grid;
    border-top: 1px solid var(--line);
}

.concept-flow div {
    display: grid;
    grid-template-columns: 52px minmax(0, 1fr);
    gap: 18px;
    padding: 18px 0;
    border-bottom: 1px solid var(--line);
}

.concept-flow span {
    color: var(--accent);
    font: 760 11px/1.5 var(--mono);
}

.concept-flow p {
    margin: 0;
    color: var(--ink);
    font-size: 14px;
    min-width: 0;
}

.knowledge-grid {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    gap: 14px;
}

.knowledge-grid article {
    min-height: 210px;
    padding: 20px;
    border: 1px solid var(--line);
    border-radius: var(--radius-sm);
    background: var(--surface-2);
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, .42);
}

.knowledge-grid article > span {
    color: var(--accent);
    font: 760 10px/1 var(--mono);
}

.knowledge-grid h3 {
    margin: 24px 0 10px;
    color: var(--ink);
    font-size: 17px;
    line-height: 1.35;
}

.knowledge-grid p {
    margin: 0;
    color: color-mix(in srgb, var(--text) 88%, var(--muted));
    font-size: 13px;
    line-height: 1.85;
}

.lesson-list {
    display: grid;
    gap: 10px;
}

.lesson-list article {
    display: grid;
    grid-template-columns: 44px 1fr;
    gap: 14px;
    padding: 16px 0;
    border-top: 1px solid var(--line);
}

.lesson-list article:last-child {
    border-bottom: 1px solid var(--line);
}

.lesson-list article > span {
    color: var(--accent);
    font: 760 10px/1.9 var(--mono);
}

.lesson-list p {
    margin: 0;
    color: color-mix(in srgb, var(--text) 90%, var(--muted));
    font-size: 14px;
    line-height: 1.85;
}

.checklist-list article > span {
    color: var(--success);
}

.code-panel {
    overflow: hidden;
    border: 1px solid #252b28;
    border-radius: 16px;
    background: #171b19;
    box-shadow: var(--shadow-small);
}

.code-head {
    display: flex;
    align-items: center;
    justify-content: space-between;
    min-height: 44px;
    padding: 0 15px;
    border-bottom: 1px solid rgba(255, 255, 255, .08);
    color: #aeb7b0;
    font: 700 10px/1 var(--mono);
    letter-spacing: .1em;
    text-transform: uppercase;
}

.code-head button {
    border: 0;
    background: transparent;
    color: #d9e4dc;
    font-size: 11px;
    cursor: pointer;
}

.code-panel pre {
    margin: 0;
    padding: 24px;
    overflow: auto;
    color: #e8eee9;
    font: 13px/1.8 var(--mono);
    tab-size: 4;
}

.code-explain {
    margin-top: 14px;
    padding: 17px 18px;
    border-left: 3px solid var(--accent);
    border-radius: 0 12px 12px 0;
    background: var(--accent-soft);
}

.expected-output {
    margin-top: 14px;
    padding: 16px 18px;
    border: 1px solid var(--line);
    border-radius: 12px;
    background: var(--surface-2);
}

.expected-output strong {
    display: block;
    color: var(--ink);
    font-size: 12px;
}

.expected-output ul {
    display: grid;
    gap: 8px;
    margin: 10px 0 0;
    padding-left: 18px;
}

.expected-output li {
    color: var(--muted);
    font-size: 13px;
    line-height: 1.65;
}

.code-explain strong {
    color: var(--ink);
    font-size: 12px;
}

.code-explain p {
    margin: 5px 0 0;
    font-size: 13px;
    line-height: 1.7;
}

.mistake-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
}

.mistake-grid article,
.practice-list article {
    padding: 18px;
}

.mistake-grid article {
    min-height: 190px;
}

.mistake-grid article > span {
    color: var(--danger);
    font: 760 10px/1 var(--mono);
}

.mistake-grid h3 {
    margin: 28px 0 8px;
    color: var(--ink);
    font-size: 15px;
    line-height: 1.35;
}

.mistake-grid p {
    margin: 0;
    color: var(--muted);
    font-size: 12px;
    line-height: 1.7;
}

.practice-list {
    display: grid;
    gap: 12px;
}

.practice-list header {
    display: flex;
    align-items: center;
    gap: 10px;
}

.practice-list header span {
    display: grid;
    place-items: center;
    width: 28px;
    height: 28px;
    border-radius: 10px;
    background: var(--accent-soft);
    color: var(--accent);
    font: 760 10px/1 var(--mono);
}

.practice-list header strong {
    color: var(--ink);
    font-size: 14px;
}

.practice-list p {
    margin: 13px 0;
    font-size: 13px;
    line-height: 1.7;
}

.practice-list textarea {
    min-height: 104px;
    padding: 12px;
    resize: vertical;
    font: 13px/1.6 var(--font);
}

.answers-section details {
    border-top: 1px solid var(--line);
}

.answers-section details:last-child {
    border-bottom: 1px solid var(--line);
}

.answers-section summary {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 18px 0;
    color: var(--ink);
    font-weight: 700;
    list-style: none;
    cursor: pointer;
}

.answers-section summary::-webkit-details-marker {
    display: none;
}

.answers-section summary span {
    color: var(--accent);
    font: 760 10px/1 var(--mono);
}

.answers-section details > div {
    padding: 0 0 20px 24px;
    color: var(--muted);
}

.answers-section pre {
    overflow: auto;
    padding: 16px;
    border-radius: 12px;
    background: #171b19;
    color: #e8eee9;
    font: 12px/1.7 var(--mono);
}

.lesson-footer {
    display: flex;
    justify-content: space-between;
    gap: 12px;
    padding-top: 34px;
}

.lesson-taxonomy {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 16px;
}

.lesson-taxonomy span {
  padding: 7px 10px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
  font: 700 11px/1 var(--mono);
}

.lesson-table th,
.lesson-table td {
  padding: 14px 12px;
  border-top: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.shape-flow div,
.metric-flow div,
.debug-flow div {
  grid-template-columns: 92px minmax(0, 1fr);
}

.quality-review-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
}

.quality-card {
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  background: var(--surface-2);
}

.quality-card span {
  display: block;
  color: var(--muted);
  font: 760 10px/1 var(--mono);
  letter-spacing: .08em;
  text-transform: uppercase;
}

.quality-card strong {
  display: block;
  margin-top: 12px;
  color: var(--ink);
  font-size: 22px;
}

.quality-summary {
  margin: 16px 0 0;
  color: var(--muted);
  font-size: 13px;
}