/* =========================================================
   公共样式：章节目录页面（chapter.css）
   可复用到所有章节：第1章、第2章、第3章...
   ========================================================= */

/* ------------ 基础变量 ------------ */
:root {
    --primary: #2980b9;
    --primary-dark: #216694;
    --accent: #3498db;
    --text-main: #2c3e50;
    --text-sub: #7f8c8d;
    --bg-page: #f3f6fb;
    --card-bg: #ffffff;
    --border-muted: #e1e4eb;
}

/* 防止默认边距影响布局 */
* { box-sizing: border-box; }

/* ------------ 页面背景 ------------ */
body {
    font-family: "Microsoft YaHei", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
    background: radial-gradient(circle at top left, #eef5ff 0, #f3f6fb 40%, #edf2f7 100%);
    margin: 0;
    padding: 0;
    color: var(--text-main);
}

/* ------------ 顶部标题栏 ------------ */
.header {
    background: linear-gradient(135deg, var(--primary), #3b8fd3);
    color: white;
    padding: 18px 16px 22px;
    position: sticky;
    top: 0;
    z-index: 10;
    box-shadow: 0 4px 10px rgba(0,0,0,0.08);
}

.header-inner {
    max-width: 900px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.header-top {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 10px;
    flex-wrap: wrap;
}

.back-link {
    color: white;
    text-decoration: none;
    border: 1px solid rgba(255,255,255,0.5);
    padding: 6px 14px;
    border-radius: 999px;
    font-size: 0.85rem;
    display: inline-flex;
    align-items: center;
    gap: 4px;
    backdrop-filter: blur(3px);
    background-color: rgba(255,255,255,0.06);
    transition: background 0.2s, transform 0.1s, box-shadow 0.2s;
}

.back-link:hover {
    background-color: rgba(255,255,255,0.15);
    transform: translateY(-1px);
    box-shadow: 0 3px 8px rgba(0,0,0,0.12);
}

.header-title {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.header h1 {
    margin: 0;
    font-size: 1.4rem;
    letter-spacing: 0.04em;
}

.header p {
    margin: 0;
    opacity: 0.85;
    font-size: 0.9rem;
}

/* ------------ 主体容器 ------------ */
.container {
    max-width: 900px;
    margin: 20px auto 30px;
    padding: 0 16px 10px;
}

.chapter-subtitle {
    font-size: 0.9rem;
    color: var(--text-sub);
    margin-bottom: 10px;
}

.lesson-list {
    display: flex;
    flex-direction: column;
    gap: 14px;
}

/* ------------ 卡片 ------------ */
.lesson-card {
    background: var(--card-bg);
    border-radius: 12px;
    padding: 16px 18px 14px;
    box-shadow: 0 6px 16px rgba(15, 23, 42, 0.06);
    border: 1px solid var(--border-muted);
    display: flex;
    flex-direction: column;
    gap: 10px;
    position: relative;
    overflow: hidden;
    transition: transform 0.18s ease, box-shadow 0.18s ease, border-color 0.18s ease;
}

.lesson-card::before {
    content: "";
    position: absolute;
    inset: 0;
    border-left: 4px solid #bdc3c7; /* 默认灰色 */
    border-radius: 12px;
    pointer-events: none;
}

.lesson-card.active::before {
    border-left-color: var(--accent);
}

.lesson-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 22px rgba(15, 23, 42, 0.12);
    border-color: rgba(52,152,219,0.65);
}

.lesson-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 10px;
    flex-wrap: wrap;
}

.lesson-info h3 {
    margin: 0 0 4px;
    font-size: 1.05rem;
    color: var(--text-main);
}

.lesson-info p {
    margin: 0;
    font-size: 0.86rem;
    color: var(--text-sub);
}

/* ------------ 状态标签 ------------ */
.status-tag {
    font-size: 0.72rem;
    padding: 3px 10px;
    border-radius: 999px;
    margin-left: 6px;
    vertical-align: middle;
    border: 1px solid transparent;
    white-space: nowrap;
}

.tag-ready {
    background-color: #e8f8f5;
    color: #1e9f55;
    border-color: #27ae60;
}

.tag-todo {
    background-color: #f3f3f3;
    color: #999;
    border-color: #d0d0d0;
}

/* ------------ 按钮区域 ------------ */
.resource-group {
    margin-top: 8px;
    padding-top: 10px;
    border-top: 1px dashed #e3e7ee;
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}

/* 无资源则隐藏 */
.resource-group:empty {
    display: none;
}

/* ------------ 资源按钮 ------------ */
.res-btn {
    background-color: var(--accent);
    color: white;
    text-decoration: none;
    padding: 6px 12px;
    border-radius: 999px;
    font-size: 0.82rem;
    transition: background 0.2s, transform 0.1s, box-shadow 0.1s;
    display: inline-flex;
    align-items: center;
    gap: 4px;
    white-space: nowrap;
}

.res-btn::before {
    content: "📄";
    font-size: 0.9em;
}

.res-btn:hover {
    background-color: var(--primary-dark);
    transform: translateY(-1px);
    box-shadow: 0 3px 8px rgba(52,152,219,0.35);
}

/* ------------ 移动端优化 ------------ */
@media (max-width: 600px) {
    .header {
        padding: 14px 12px 18px;
    }

    .lesson-card {
        padding: 14px 14px 12px;
    }

    .lesson-info h3 {
        font-size: 1rem;
    }

    .lesson-info p {
        font-size: 0.8rem;
    }

    .res-btn {
        font-size: 0.78rem;
        padding: 5px 10px;
    }
}