/* ===== Chapters List Page / 教程列表页 =====
 * 用途：教程目录列表页样式
 * 负责：.chapters-header 页头、.chapters-grid 列表容器、.chapter-card 卡片
 * 使用页面：tutorial.html
 */
.chapters-header {
    text-align: center;
    padding: 72px 32px 48px;
}

.chapters-header h1 {
    font-family: var(--serif);
    font-size: 44px;
    font-weight: 500;
    letter-spacing: -1px;
    margin-bottom: 10px;
}

.chapters-header p {
    color: var(--text-light);
}

.chapters-grid {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 32px 88px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.chapter-card {
    display: block;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px 32px;
    text-decoration: none;
    color: var(--text);
    transition: border-color 0.15s, transform 0.15s;
}

.chapter-card:hover {
    border-color: var(--accent);
    transform: translateY(-1px);
}

.chapter-card h3 {
    font-family: var(--serif);
    font-size: 20px;
    font-weight: 500;
    margin-bottom: 8px;
}

/* ===== Stage 可折叠分组 ===== */
/* ---- 标题行（可点击折叠，与术语表风格一致） ---- */
.stage-section-header {
    display: flex;
    align-items: baseline;
    gap: 10px;
    cursor: pointer;
    user-select: none;
    margin-bottom: 14px;
    margin-top: 8px;
}

.stage-section:first-child .stage-section-header {
    margin-top: 0;
}

.stage-section-title {
    font-family: var(--serif);
    font-size: 22px;
    font-weight: 500;
    color: var(--text);
    padding-bottom: 6px;
    border-bottom: 2px solid var(--accent);
    display: inline-block;
    margin: 0;
}

.stage-section-count {
    font-size: 13px;
    color: var(--text-muted);
    margin-left: 4px;
}

.stage-section-arrow {
    font-size: 16px;
    color: var(--text-muted);
    transition: transform 0.25s ease;
    flex-shrink: 0;
}

.stage-section.collapsed .stage-section-arrow {
    transform: rotate(-90deg);
}

/* ---- 卡片容器（可折叠 body） ---- */
.stage-section-body {
    overflow: hidden;
    transition: height 0.3s ease;
    padding-top: 2px;
}

.stage-section-cards {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.chapter-card .chapter-date {
    font-size: 13px;
    color: var(--text-muted);
    margin-bottom: 8px;
}

.chapter-card .chapter-summary {
    font-size: 14px;
    color: var(--text-light);
    line-height: 1.6;
}

/* ===== Track 分叉区域 ===== */

/* 分叉选择提示区（导航跳转用，非列表页） */
.fork-choices {
    display: flex;
    gap: 16px;
    justify-content: center;
    padding: 32px 0;
}

.fork-choice-btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 12px 24px;
    border-radius: var(--radius);
    border: 2px solid var(--border);
    background: var(--bg-card);
    font-family: var(--sans);
    font-size: 15px;
    font-weight: 500;
    cursor: pointer;
    text-decoration: none;
    transition: border-color 0.15s, transform 0.15s;
}

.fork-choice-btn:hover {
    transform: translateY(-1px);
}

.fork-choice-btn.track-a {
    border-color: #c96342;
    color: #c96342;
}

.fork-choice-btn.track-a:hover {
    background: #fdf5f2;
}

.fork-choice-btn.track-b {
    border-color: #3b82f6;
    color: #3b82f6;
}

.fork-choice-btn.track-b:hover {
    background: #f0f6ff;
}

/* ---- 教程列表页：两列 Track 布局 ---- */
.track-split {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
}

.track-column {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
}

.track-column-header {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 16px;
    padding-bottom: 12px;
    border-bottom: 2px solid var(--border-strong);
}

.track-column-header.track-a {
    border-bottom-color: #c96342;
}

.track-column-header.track-b {
    border-bottom-color: #3b82f6;
}

.track-column-title {
    font-family: var(--serif);
    font-size: 18px;
    font-weight: 600;
    margin: 0;
}

.track-column-header.track-a .track-column-title {
    color: #c96342;
}

.track-column-header.track-b .track-column-title {
    color: #3b82f6;
}

.track-column-count {
    font-size: 12px;
    color: var(--text-muted);
}

.track-column .chapter-card {
    padding: 16px 20px;
}

.track-column .chapter-card h3 {
    font-size: 16px;
}

.track-column .stage-section-cards {
    gap: 6px;
}

/* track 参数高亮/弱化 */
.track-column.dimmed {
    opacity: 0.4;
    transition: opacity 0.3s;
}

.track-column.highlighted {
    opacity: 1;
    box-shadow: 0 0 0 2px var(--accent);
    transition: opacity 0.3s, box-shadow 0.3s;
}

/* ---- Track 标签 ---- */
.track-badge {
    display: inline-block;
    font-family: var(--sans);
    font-size: 11px;
    font-weight: 600;
    padding: 2px 8px;
    border-radius: 100px;
    vertical-align: middle;
    margin-left: 8px;
}

.track-badge.shared {
    background: #f3f1ea;
    color: #6b6a66;
}

.track-badge.track-a {
    background: #fdf5f2;
    color: #c96342;
}

.track-badge.track-b {
    background: #f0f6ff;
    color: #3b82f6;
}

/* 共用区域标签行 */
.stage-section-track-label {
    font-family: var(--sans);
    font-size: 12px;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: 6px;
}

/* 响应式：窄屏单列 */
@media (max-width: 640px) {
    .track-split {
        grid-template-columns: 1fr;
    }
}