/* ============================================
   英语小课堂 — 全站样式
   专为 K12 学生设计，清新活泼风格
   ============================================ */

/* ---------- 基础重置 ---------- */
*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; font-size: 16px; }

body {
    font-family: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
    color: #2d3436;
    background: #fafbfc;
    line-height: 1.7;
    -webkit-font-smoothing: antialiased;
}

a { text-decoration: none; color: inherit; transition: color .2s; }
img { max-width: 100%; display: block; }
ul, ol { list-style: none; }

.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }

/* ---------- 导航栏 ---------- */
.navbar {
    position: fixed; top: 0; left: 0; right: 0; z-index: 1000;
    background: rgba(255,255,255,0.95);
    backdrop-filter: blur(20px);
    border-bottom: 1px solid #eef1f5;
    transition: box-shadow .3s;
}
.navbar.scrolled { box-shadow: 0 2px 20px rgba(0,0,0,0.08); }

.nav-container {
    max-width: 1200px; margin: 0 auto; padding: 0 20px;
    display: flex; align-items: center; justify-content: space-between;
    height: 64px;
}

.logo { display: flex; align-items: center; gap: 10px; font-weight: 700; text-decoration: none; }
.logo-icon { font-size: 28px; }
.logo-icon-img { height: 36px; width: 36px; object-fit: contain; flex-shrink: 0; }
.logo-text { font-size: 20px; color: #2d3436; font-family: 'Noto Sans SC', sans-serif; white-space: nowrap; }

.nav-links { display: flex; align-items: center; gap: 4px; }
.nav-links > li > a {
    padding: 8px 16px; border-radius: 8px; font-size: 15px; font-weight: 500;
    color: #555; transition: all .2s;
}
.nav-links > li > a:hover, .nav-links > li > a.active {
    color: #4f7cff; background: rgba(79,124,255,0.08);
}

/* 下拉菜单 */
.nav-dropdown { position: relative; }
.nav-dropdown > a { cursor: pointer; display: flex; align-items: center; gap: 4px; }
.dropdown-menu {
    position: absolute; top: calc(100% + 8px); left: 50%; transform: translateX(-50%);
    background: #fff; border-radius: 12px; box-shadow: 0 8px 30px rgba(0,0,0,0.12);
    padding: 8px; min-width: 200px; opacity: 0; visibility: hidden;
    transition: all .2s; transform: translateX(-50%) translateY(8px);
}
.nav-dropdown:hover .dropdown-menu { opacity: 1; visibility: visible; transform: translateX(-50%) translateY(0); }
.dropdown-menu a {
    display: block; padding: 10px 16px; border-radius: 8px; font-size: 14px; color: #555;
}
.dropdown-menu a:hover { background: #f0f4ff; color: #4f7cff; }

/* 移动端菜单按钮 */
.mobile-menu-btn {
    display: none; flex-direction: column; gap: 5px; background: none; border: none;
    cursor: pointer; padding: 10px; border-radius: 10px; transition: background .2s;
}
.mobile-menu-btn:hover { background: rgba(79,124,255,0.08); }
.mobile-menu-btn span {
    display: block; width: 22px; height: 2.5px; background: #333; border-radius: 2px;
    transition: all .3s;
}

/* ---------- Hero 区域 ---------- */
.hero {
    min-height: 100vh; display: flex; align-items: center; justify-content: center;
    text-align: center; padding: 120px 20px 80px; position: relative; overflow: hidden;
    background: linear-gradient(160deg, #f8f9ff 0%, #eef2ff 30%, #f0f7ff 60%, #faf5ff 100%);
}
.hero-bg-shapes { position: absolute; inset: 0; pointer-events: none; }
.shape {
    position: absolute; border-radius: 50%; opacity: 0.15;
    animation: float 8s ease-in-out infinite;
}
.shape-1 { width: 300px; height: 300px; background: #4f7cff; top: -80px; right: -60px; }
.shape-2 { width: 200px; height: 200px; background: #ff6b9d; bottom: -40px; left: -40px; animation-delay: -3s; }
.shape-3 { width: 150px; height: 150px; background: #43e97b; top: 40%; left: 10%; animation-delay: -5s; }
@keyframes float {
    0%, 100% { transform: translateY(0) rotate(0deg); }
    50% { transform: translateY(-20px) rotate(5deg); }
}

.hero-content { position: relative; max-width: 720px; }
.hero-badge {
    display: inline-block; padding: 8px 20px; border-radius: 50px;
    background: rgba(79,124,255,0.1); color: #4f7cff; font-size: 14px;
    font-weight: 500; margin-bottom: 24px;
}
.hero h1 {
    font-size: 3.2rem; font-weight: 900; line-height: 1.3;
    color: #1a1a2e; margin-bottom: 20px;
}
.gradient-text {
    background: linear-gradient(135deg, #4f7cff, #a855f7, #ff6b9d);
    -webkit-background-clip: text; -webkit-text-fill-color: transparent;
    background-clip: text;
}
.hero-desc { font-size: 17px; color: #666; margin-bottom: 36px; line-height: 1.8; }
.hero-actions { display: flex; gap: 16px; justify-content: center; flex-wrap: wrap; margin-bottom: 48px; }

/* 按钮 */
.btn {
    display: inline-flex; align-items: center; gap: 8px;
    padding: 12px 28px; border-radius: 10px; font-size: 15px; font-weight: 600;
    transition: all .25s; cursor: pointer; border: none;
}
.btn-primary {
    background: linear-gradient(135deg, #4f7cff, #6c5ce7);
    color: #fff; box-shadow: 0 4px 15px rgba(79,124,255,0.3);
}
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 6px 25px rgba(79,124,255,0.4); }
.btn-outline {
    background: #fff; color: #4f7cff;
    border: 2px solid #e0e7ff;
}
.btn-outline:hover { background: #f0f4ff; border-color: #4f7cff; }

/* 统计数字 */
.hero-stats { display: flex; justify-content: center; gap: 48px; }
.stat { text-align: center; }
.stat-number {
    display: block; font-size: 2rem; font-weight: 900;
    font-family: 'Quicksand', sans-serif; color: #4f7cff;
}
.stat-label { font-size: 13px; color: #888; }

/* ---------- 通用 Section ---------- */
.section { padding: 80px 0; }
.section-header { text-align: center; margin-bottom: 48px; }
.section-tag {
    display: inline-block; padding: 6px 16px; border-radius: 50px;
    background: rgba(79,124,255,0.08); color: #4f7cff; font-size: 13px;
    font-weight: 500; margin-bottom: 16px;
}
.section-header h2 { font-size: 2rem; font-weight: 800; margin-bottom: 12px; color: #1a1a2e; }
.section-header p { font-size: 16px; color: #777; max-width: 520px; margin: 0 auto; }

/* ---------- 年级卡片 ---------- */
.grade-cards { display: grid; grid-template-columns: repeat(4, 1fr); gap: 24px; }
.grade-card {
    background: #fff; border-radius: 20px; padding: 36px 28px; text-align: center;
    border: 2px solid #eef1f5; transition: all .3s; position: relative; overflow: hidden;
}
.grade-card:hover { transform: translateY(-6px); box-shadow: 0 12px 40px rgba(0,0,0,0.08); }
.grade-primary:hover { border-color: #43e97b; }
.grade-middle:hover { border-color: #4f7cff; }
.grade-high:hover { border-color: #a855f7; }

.grade-icon { font-size: 48px; margin-bottom: 12px; }
.grade-card h3 { font-size: 1.4rem; font-weight: 800; margin-bottom: 4px; }
.grade-range { font-size: 14px; color: #999; margin-bottom: 20px; }
.grade-topics { display: flex; flex-wrap: wrap; gap: 8px; justify-content: center; }
.topic-tag {
    display: inline-block; padding: 4px 12px; border-radius: 50px; font-size: 12px;
    background: #f5f7fa; color: #555;
}
.grade-arrow {
    position: absolute; top: 50%; right: 24px; transform: translateY(-50%);
    font-size: 24px; color: #ccc; transition: all .3s;
}
.grade-card:hover .grade-arrow { color: #4f7cff; transform: translateY(-50%) translateX(4px); }

/* ---------- 每日一句 ---------- */
.daily-section { padding: 40px 0; }
.daily-card {
    max-width: 800px; margin: 0 auto; background: #fff; border-radius: 20px;
    padding: 40px 48px; text-align: center; border: 2px solid #eef1f5;
    box-shadow: 0 4px 20px rgba(0,0,0,0.04);
}
.daily-label { font-size: 14px; color: #4f7cff; font-weight: 600; margin-bottom: 16px; }
.daily-quote {
    font-size: 1.4rem; font-family: 'Quicksand', 'Noto Sans SC', sans-serif;
    font-style: italic; color: #333; margin-bottom: 12px; line-height: 1.6;
}
.daily-translation { font-size: 15px; color: #666; margin-bottom: 8px; }
.daily-author { font-size: 13px; color: #999; margin-bottom: 28px; }
.daily-word {
    display: inline-flex; align-items: center; gap: 12px; flex-wrap: wrap;
    padding: 16px 24px; background: #f8f9ff; border-radius: 12px;
}
.word-label { font-size: 13px; color: #4f7cff; font-weight: 600; }
.word-en {
    font-size: 1.3rem; font-weight: 800; color: #1a1a2e;
    font-family: 'Quicksand', sans-serif;
}
.word-phonetic { font-size: 14px; color: #888; font-family: 'Quicksand', sans-serif; }
.word-cn { font-size: 14px; color: #555; }

/* ---------- 学习板块 ---------- */
.topic-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.topic-grid .topic-card:nth-child(4),
.topic-grid .topic-card:nth-child(5) { grid-column: span 1; }

.topic-card {
    background: #fff; border-radius: 20px; padding: 32px 24px; text-align: center;
    border: 2px solid #eef1f5; transition: all .3s;
}
.topic-card:hover { transform: translateY(-4px); box-shadow: 0 8px 30px rgba(0,0,0,0.08); border-color: #4f7cff; }
.topic-icon { font-size: 40px; margin-bottom: 12px; }
.topic-card h3 { font-size: 1.15rem; font-weight: 700; margin-bottom: 8px; }
.topic-card p { font-size: 14px; color: #777; margin-bottom: 16px; line-height: 1.7; }
.topic-examples { display: flex; gap: 6px; justify-content: center; flex-wrap: wrap; }
.topic-examples span {
    padding: 3px 10px; border-radius: 50px; font-size: 12px;
    background: #f0f4ff; color: #4f7cff;
}

/* ---------- 精选文章 ---------- */
.article-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 24px; }
.article-card {
    background: #fff; border-radius: 16px; overflow: hidden;
    border: 1px solid #eef1f5; transition: all .3s;
}
.article-card:hover { transform: translateY(-4px); box-shadow: 0 8px 30px rgba(0,0,0,0.1); }

.article-card-img {
    height: 140px; display: flex; align-items: flex-start; justify-content: space-between;
    padding: 16px 20px; position: relative;
}
.card-category {
    background: rgba(255,255,255,0.25); color: #fff; padding: 4px 14px;
    border-radius: 50px; font-size: 12px; font-weight: 600; backdrop-filter: blur(4px);
}
.card-grade {
    background: rgba(255,255,255,0.25); color: #fff; padding: 4px 12px;
    border-radius: 50px; font-size: 11px; backdrop-filter: blur(4px);
}
.article-card-body { padding: 20px 24px 24px; }
.article-card-body h3 { font-size: 1.1rem; font-weight: 700; margin-bottom: 8px; line-height: 1.5; }
.article-card-body p { font-size: 14px; color: #777; line-height: 1.7; margin-bottom: 12px; }
.article-meta { display: flex; gap: 16px; font-size: 12px; color: #aaa; }
.article-date { color: #bbb; }

.section-footer { text-align: center; margin-top: 40px; }

/* ---------- 学习路径 ---------- */
.path-steps { display: flex; align-items: center; justify-content: center; gap: 0; }
.path-step {
    text-align: center; flex: 0 0 auto; max-width: 200px; padding: 0 16px;
}
.step-number {
    width: 56px; height: 56px; border-radius: 50%; display: flex; align-items: center;
    justify-content: center; font-size: 1.3rem; font-weight: 800;
    background: linear-gradient(135deg, #4f7cff, #6c5ce7); color: #fff;
    margin: 0 auto 16px; font-family: 'Quicksand', sans-serif;
}
.path-step h3 { font-size: 1rem; font-weight: 700; margin-bottom: 6px; }
.path-step p { font-size: 13px; color: #888; line-height: 1.6; }
.path-connector {
    width: 60px; height: 3px; background: linear-gradient(90deg, #4f7cff, #e0e7ff);
    border-radius: 2px; margin-bottom: 30px; flex-shrink: 0;
}

/* ---------- 页面顶部 Hero ---------- */
.page-hero {
    padding: 120px 20px 60px; text-align: center;
    background: linear-gradient(160deg, #f8f9ff 0%, #eef2ff 100%);
}
.page-hero h1 { font-size: 2.4rem; font-weight: 900; margin-bottom: 8px; }
.page-hero p { font-size: 16px; color: #777; }

/* ---------- 筛选栏 ---------- */
.filter-bar {
    background: #fff; border-bottom: 1px solid #eef1f5;
    padding: 16px 0; position: sticky; top: 64px; z-index: 100;
}
.filter-group { display: flex; align-items: center; gap: 8px; margin-bottom: 8px; }
.filter-group:last-child { margin-bottom: 0; }
.filter-label { font-size: 14px; font-weight: 600; color: #555; margin-right: 4px; white-space: nowrap; }
.filter-btn {
    padding: 6px 16px; border-radius: 50px; font-size: 13px; font-weight: 500;
    border: 1.5px solid #e5e7eb; background: #fff; color: #666; cursor: pointer;
    transition: all .2s; white-space: nowrap;
}
.filter-btn:hover { border-color: #4f7cff; color: #4f7cff; }
.filter-btn.active { background: #4f7cff; color: #fff; border-color: #4f7cff; }

/* ---------- 文章列表 ---------- */
.articles-list { display: grid; grid-template-columns: repeat(2, 1fr); gap: 24px; }
.empty-state { text-align: center; padding: 60px 20px; }
.empty-icon { font-size: 64px; margin-bottom: 16px; }
.empty-state p { font-size: 16px; color: #999; margin-bottom: 20px; }

/* ---------- 文章页 Hero ---------- */
.article-hero {
    padding: 120px 20px 60px; color: #fff;
}
.article-hero-tags { display: flex; gap: 8px; margin-bottom: 16px; }
.tag {
    padding: 4px 14px; border-radius: 50px; font-size: 13px; font-weight: 500;
    background: rgba(255,255,255,0.2); backdrop-filter: blur(4px);
}
.article-hero h1 { font-size: 2.2rem; font-weight: 900; margin-bottom: 12px; }
.article-hero-desc { font-size: 16px; opacity: 0.9; margin-bottom: 16px; max-width: 600px; }
.article-hero-meta { display: flex; gap: 20px; font-size: 14px; opacity: 0.8; }

/* ---------- 文章内容 ---------- */
.article-content { background: #fafbfc; }
.article-body {
    max-width: 800px; margin: 0 auto; padding: 40px 20px 60px;
}

.article-body h2 {
    font-size: 1.6rem; font-weight: 800; margin: 40px 0 16px; padding-bottom: 8px;
    border-bottom: 3px solid #4f7cff; color: #1a1a2e;
}
.article-body h3 { font-size: 1.2rem; font-weight: 700; margin: 28px 0 12px; color: #333; }
.article-body p { margin-bottom: 14px; color: #444; line-height: 1.9; }
.article-body strong { color: #1a1a2e; }
.article-body em { color: #4f7cff; font-style: italic; }

/* 目录 */
.toc {
    background: #fff; border-radius: 16px; padding: 24px 28px; margin-bottom: 32px;
    border: 2px solid #eef1f5;
}
.toc h3 { font-size: 1rem; font-weight: 700; margin-bottom: 12px; color: #1a1a2e; }
.toc ol { padding-left: 20px; }
.toc li { margin-bottom: 6px; list-style: decimal; }
.toc a { color: #4f7cff; font-size: 14px; }
.toc a:hover { text-decoration: underline; }

/* 时态卡片 */
.tense-card {
    background: #fff; border-radius: 16px; padding: 24px 28px; margin-bottom: 24px;
    border: 1.5px solid #eef1f5; box-shadow: 0 2px 10px rgba(0,0,0,0.03);
}
.tense-header {
    display: flex; align-items: center; justify-content: space-between;
    margin-bottom: 16px; padding-bottom: 12px; border-bottom: 2px solid #f0f4ff;
}
.tense-name { font-size: 1.2rem; font-weight: 800; color: #1a1a2e; }
.tense-structure {
    padding: 4px 14px; border-radius: 50px; font-size: 13px; font-weight: 600;
    background: #f0f4ff; color: #4f7cff; font-family: 'Quicksand', monospace;
}
.tense-card p { margin-bottom: 10px; }

/* 例句框 */
.example-box {
    background: #f8faff; border-radius: 12px; padding: 20px 24px; margin: 16px 0;
    border-left: 4px solid #4f7cff;
}
.example-header { font-weight: 700; font-size: 14px; margin-bottom: 10px; color: #333; }
.example-box p { margin-bottom: 6px; font-size: 15px; line-height: 1.7; }
.example-box .cn { color: #888; font-size: 14px; padding-left: 16px; }

/* 提示框 */
.tip-box {
    background: #fffbeb; border-radius: 12px; padding: 20px 24px; margin: 16px 0;
    border-left: 4px solid #f59e0b;
}
.tip-box strong { color: #92400e; }

/* 总结表格 */
.summary-table { margin: 24px 0; overflow-x: auto; }
.summary-table table {
    width: 100%; border-collapse: collapse; font-size: 14px; background: #fff;
    border-radius: 12px; overflow: hidden; box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
.summary-table th {
    background: #4f7cff; color: #fff; padding: 12px 16px; font-weight: 600;
    text-align: left; white-space: nowrap;
}
.summary-table td { padding: 10px 16px; border-bottom: 1px solid #f0f4ff; }
.summary-table tr:nth-child(even) td { background: #fafbff; }
.summary-table tr:hover td { background: #f0f4ff; }

/* 练习题 */
.practice-box {
    background: linear-gradient(135deg, #f0f4ff, #faf5ff); border-radius: 16px;
    padding: 28px; margin: 32px 0; border: 2px solid #e0e7ff;
}
.practice-box h3 { font-size: 1.2rem; font-weight: 800; margin-bottom: 16px; }
.practice-box ol { padding-left: 20px; }
.practice-box li { list-style: decimal; margin-bottom: 16px; font-size: 15px; line-height: 1.7; }
.practice-box details {
    margin-top: 6px; padding: 10px 16px; background: #fff; border-radius: 8px;
    cursor: pointer;
}
.practice-box summary { color: #4f7cff; font-size: 14px; font-weight: 500; }

/* 词汇卡片网格 */
.vocab-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 12px; margin: 20px 0; }
.vocab-item {
    background: #fff; border-radius: 12px; padding: 16px 20px;
    border: 1.5px solid #eef1f5; transition: all .2s;
}
.vocab-item:hover { border-color: #4f7cff; box-shadow: 0 4px 12px rgba(79,124,255,0.08); }

/* TTS 朗读按钮 */
.tts-btn {
    position: absolute; top: 8px; right: 8px;
    width: 32px; height: 32px; border-radius: 50%;
    background: linear-gradient(135deg, #4f7cff, #764ba2);
    border: none; cursor: pointer; font-size: 14px;
    display: flex; align-items: center; justify-content: center;
    box-shadow: 0 2px 8px rgba(79,124,255,0.3);
    transition: all .2s; z-index: 2; padding: 0;
}
.tts-btn:hover { transform: scale(1.15); box-shadow: 0 4px 14px rgba(79,124,255,0.4); }
.tts-btn:active { transform: scale(0.95); }
.tts-btn.speaking {
    background: linear-gradient(135deg, #e74c3c, #c0392b);
    animation: tts-pulse 1s infinite;
}
@keyframes tts-pulse {
    0%, 100% { box-shadow: 0 2px 8px rgba(231,76,60,0.3); }
    50% { box-shadow: 0 2px 20px rgba(231,76,60,0.6); }
}
/* 可点击朗读的文本 */
.tts-speak { cursor: pointer; transition: color .2s; }
.tts-speak:hover { color: #4f7cff; }
.tts-speak.speaking { color: #e74c3c; }
.vocab-en {
    display: block; font-size: 1.1rem; font-weight: 800; color: #1a1a2e;
    font-family: 'Quicksand', sans-serif; margin-bottom: 2px;
}
.vocab-phonetic { font-size: 12px; color: #999; font-family: 'Quicksand', sans-serif; }
.vocab-cn { font-size: 14px; color: #555; font-weight: 500; }
.vocab-example {
    display: block; font-size: 13px; color: #4f7cff; margin-top: 6px;
    font-style: italic;
}

/* 颜色卡片 */
.color-grid { display: flex; flex-wrap: wrap; gap: 12px; margin: 20px 0; }
.color-item {
    display: flex; align-items: center; gap: 10px; background: #fff;
    padding: 10px 16px; border-radius: 10px; border: 1.5px solid #eef1f5;
    font-size: 14px;
}
.color-swatch { width: 28px; height: 28px; border-radius: 50%; flex-shrink: 0; }

/* 创作中 */
.coming-soon { text-align: center; padding: 80px 20px; }
.coming-soon-icon { font-size: 80px; margin-bottom: 20px; }
.coming-soon h2 { font-size: 1.6rem; font-weight: 800; margin-bottom: 12px; color: #333; }
.coming-soon p { font-size: 15px; color: #888; margin-bottom: 8px; }
.coming-soon .btn { margin-top: 24px; }

/* 文章导航 */
.article-nav {
    display: flex; justify-content: space-between; align-items: center;
    margin-top: 40px; padding-top: 32px; border-top: 2px solid #eef1f5;
    flex-wrap: wrap; gap: 12px;
}

/* ---------- 关于页面 ---------- */
.about-story {
    display: grid; grid-template-columns: 1fr 1fr; gap: 48px; align-items: center;
}
.story-content h2 { font-size: 2rem; font-weight: 800; margin-bottom: 20px; }
.story-content p { font-size: 15px; color: #555; line-height: 1.9; margin-bottom: 14px; }
.story-card {
    background: linear-gradient(135deg, #4f7cff, #6c5ce7); border-radius: 20px;
    padding: 48px 32px; text-align: center; color: #fff;
}
.story-emoji { font-size: 64px; margin-bottom: 16px; }
.story-card h3 { font-size: 1.4rem; margin-bottom: 8px; }
.story-card p { font-size: 16px; opacity: 0.9; }

/* 数据统计 */
.stats-section { background: #f8f9ff; }
.stats-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 24px; }
.stat-card {
    text-align: center; background: #fff; border-radius: 16px; padding: 28px 16px;
    border: 1.5px solid #eef1f5;
}
.stat-icon { font-size: 36px; margin-bottom: 8px; }
.stat-card .stat-number {
    font-size: 2.2rem; font-weight: 900; color: #4f7cff;
    font-family: 'Quicksand', sans-serif;
}
.stat-card .stat-label { font-size: 14px; color: #888; margin-top: 4px; }

/* 特色 */
.features-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.feature-card {
    background: #fff; border-radius: 16px; padding: 28px 24px;
    border: 1.5px solid #eef1f5; transition: all .3s;
}
.feature-card:hover { transform: translateY(-4px); box-shadow: 0 8px 25px rgba(0,0,0,0.06); border-color: #4f7cff; }
.feature-icon { font-size: 36px; margin-bottom: 12px; }
.feature-card h3 { font-size: 1.05rem; font-weight: 700; margin-bottom: 8px; }
.feature-card p { font-size: 14px; color: #777; line-height: 1.7; }

/* 时间线 */
.timeline { max-width: 600px; margin: 0 auto; position: relative; padding-left: 40px; }
.timeline::before {
    content: ''; position: absolute; left: 15px; top: 0; bottom: 0;
    width: 3px; background: linear-gradient(to bottom, #4f7cff, #e0e7ff);
    border-radius: 2px;
}
.timeline-item { position: relative; margin-bottom: 36px; }
.timeline-item:last-child { margin-bottom: 0; }
.timeline-dot {
    position: absolute; left: -33px; top: 4px; width: 12px; height: 12px;
    background: #4f7cff; border-radius: 50%; border: 3px solid #fff;
    box-shadow: 0 0 0 3px rgba(79,124,255,0.2);
}
.timeline-date { font-size: 13px; color: #4f7cff; font-weight: 600; }
.timeline-content h3 { font-size: 1.1rem; font-weight: 700; margin: 4px 0 6px; }
.timeline-content p { font-size: 14px; color: #777; line-height: 1.7; }

/* 联系我们 */
.contact-card {
    background: #fff; border-radius: 20px; padding: 48px; text-align: center;
    border: 2px solid #eef1f5; max-width: 600px; margin: 0 auto;
}
.contact-card h2 { font-size: 1.6rem; font-weight: 800; margin-bottom: 12px; }
.contact-card > p { font-size: 15px; color: #777; margin-bottom: 8px; }
.contact-items { display: flex; justify-content: center; gap: 32px; margin-top: 24px; flex-wrap: wrap; }
.contact-item {
    display: flex; align-items: center; gap: 8px; font-size: 15px; color: #555;
}
.contact-icon { font-size: 20px; }

/* ---------- 页脚 ---------- */
.footer {
    background: #1a1a2e; color: #fff; padding: 60px 0 0;
}
.footer-content {
    display: grid; grid-template-columns: 2fr 1fr 1fr 1fr; gap: 40px;
    padding-bottom: 40px; border-bottom: 1px solid rgba(255,255,255,0.1);
}
.footer-brand .logo-text { color: #fff; font-size: 20px; }
.footer-brand p { font-size: 13px; color: rgba(255,255,255,0.5); margin-top: 8px; line-height: 1.7; }
.footer-links h4 { font-size: 14px; font-weight: 600; margin-bottom: 16px; }
.footer-links a { display: block; font-size: 13px; color: rgba(255,255,255,0.6); margin-bottom: 8px; }
.footer-links a:hover { color: #fff; }
.footer-bottom { text-align: center; padding: 20px 0; }
.footer-bottom p { font-size: 13px; color: rgba(255,255,255,0.4); }

/* ---------- 响应式 ---------- */
@media (max-width: 900px) {
    .grade-cards, .topic-grid, .features-grid { grid-template-columns: repeat(2, 1fr); }
    .article-grid, .articles-list { grid-template-columns: repeat(2, 1fr); }
    .about-story { grid-template-columns: 1fr; }
    .stats-grid { grid-template-columns: repeat(2, 1fr); }
    .footer-content { grid-template-columns: 1fr 1fr; gap: 32px; }
    .hero h1 { font-size: 2.2rem; }
    .path-steps { flex-direction: column; }
    .path-connector { width: 3px; height: 40px; margin: 0 auto; }
    .vocab-grid { grid-template-columns: repeat(2, 1fr); }
    .container { padding: 0 16px; }
}

@media (max-width: 768px) {
    .grade-cards { grid-template-columns: repeat(2, 1fr); gap: 14px; }
    .grade-card { padding: 24px 16px; border-radius: 16px; }
    .grade-icon { font-size: 36px; margin-bottom: 8px; }
    .grade-card h3 { font-size: 1.15rem; }
    .grade-topics { gap: 5px; }
    .topic-tag { font-size: 11px; padding: 3px 9px; }
    .grade-arrow { display: none; }
    .topic-grid { grid-template-columns: 1fr; gap: 14px; }
    .topic-card { padding: 24px 18px; border-radius: 16px; }
    .topic-icon { font-size: 32px; }
}

@media (max-width: 640px) {
    /* ---- 移动端导航 ---- */
    .nav-links { display: none; }
    .nav-links.open {
        display: flex; flex-direction: column; position: absolute;
        top: 64px; left: 0; right: 0; background: #fff;
        padding: 8px 12px 16px; box-shadow: 0 10px 30px rgba(0,0,0,0.12);
        border-bottom-left-radius: 20px; border-bottom-right-radius: 20px;
        gap: 2px; max-height: calc(100vh - 64px); overflow-y: auto;
    }
    .nav-links.open > li > a {
        display: flex; align-items: center; gap: 8px;
        padding: 14px 16px; border-radius: 12px; font-size: 15px; font-weight: 500;
        color: #444; transition: all .2s;
    }
    .nav-links.open > li > a:active {
        background: rgba(79,124,255,0.08); color: #4f7cff;
    }
    .nav-links.open > li > a.active {
        background: linear-gradient(135deg, rgba(79,124,255,0.12), rgba(108,92,231,0.08));
        color: #4f7cff; font-weight: 600;
    }
    /* 移动端下拉菜单 */
    .nav-links.open .nav-dropdown .dropdown-menu {
        position: static; transform: none; opacity: 1; visibility: visible;
        box-shadow: none; border: none; padding: 0 0 0 24px; min-width: auto;
        display: none;
    }
    .nav-links.open .nav-dropdown .dropdown-menu.show { display: block; }
    .nav-links.open .nav-dropdown .dropdown-menu a {
        padding: 10px 14px; font-size: 14px; border-radius: 10px; color: #666;
    }
    .nav-links.open .nav-dropdown > a::after {
        content: ''; display: inline-block; width: 0; height: 0;
        border-left: 5px solid transparent; border-right: 5px solid transparent;
        border-top: 5px solid #aaa; margin-left: auto; transition: transform .2s;
    }
    .nav-links.open .nav-dropdown.open > a::after {
        transform: rotate(180deg); border-top-color: #4f7cff;
    }
    .mobile-menu-btn { display: flex; }

    /* ---- 移动端 Hero ---- */
    .hero { min-height: auto; padding: 80px 20px 40px; }
    .hero h1 { font-size: 1.65rem; line-height: 1.35; margin-bottom: 14px; }
    .hero-desc { font-size: 14px; line-height: 1.7; margin-bottom: 24px; }
    .hero-badge { font-size: 12px; padding: 6px 14px; margin-bottom: 16px; }
    .hero-stats { gap: 24px; margin-top: 20px; }
    .stat-number { font-size: 1.3rem; }
    .stat-label { font-size: 11px; }
    .hero-actions { gap: 12px; margin-bottom: 0; }
    .btn { padding: 11px 22px; font-size: 14px; border-radius: 10px; }

    /* ---- 移动端 Section ---- */
    .section { padding: 36px 0; }
    .section-header { margin-bottom: 24px; }
    .section-header h2 { font-size: 1.35rem; }
    .section-header p { font-size: 14px; }
    .section-tag { font-size: 12px; padding: 5px 12px; }
    .page-hero { padding: 76px 20px 28px; }
    .page-hero h1 { font-size: 1.45rem; }

    /* ---- 移动端卡片 ---- */
    .article-grid, .articles-list { grid-template-columns: 1fr; gap: 14px; }
    .daily-card { padding: 24px 20px; border-radius: 16px; }
    .daily-quote { font-size: 1rem; }
    .daily-word { flex-direction: column; align-items: flex-start; padding: 14px 18px; }
    .contact-card { padding: 28px 20px; border-radius: 16px; }
    .contact-items { flex-direction: column; align-items: center; gap: 14px; }
    .filter-group { flex-wrap: wrap; gap: 6px; }
    .filter-btn { padding: 6px 13px; font-size: 12px; }
    .features-grid { grid-template-columns: 1fr; gap: 14px; }
    .feature-card { padding: 20px; border-radius: 16px; }
    .timeline-content { padding: 14px; }
    .stats-grid { grid-template-columns: repeat(2, 1fr); gap: 12px; }
    .stat-card { padding: 16px; border-radius: 14px; }
    .footer-content { grid-template-columns: 1fr; gap: 24px; }
    .vocab-grid { grid-template-columns: repeat(2, 1fr); gap: 10px; }
    .container { padding: 0 16px; }
    body { overflow-x: hidden; }
}