/* 全局样式 */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    min-height: 100vh;
    color: #333;
}
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}
a {
    text-decoration: none;
    color: inherit;
}

/* 导航栏 */
.navbar {
    background: rgba(255,255,255,0.95);
    backdrop-filter: blur(10px);
    box-shadow: 0 2px 20px rgba(0,0,0,0.1);
    position: sticky;
    top: 0;
    z-index: 1000;
}
.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
    height: 70px;
}
.nav-logo {
    font-size: 1.8rem;
    font-weight: 700;
    background: linear-gradient(45deg, #667eea, #764ba2);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}
.nav-menu {
    display: flex;
    list-style: none;
    gap: 25px;
}
.nav-menu a {
    font-weight: 500;
    transition: color 0.3s;
    padding: 5px 0;
    border-bottom: 2px solid transparent;
}
.nav-menu a:hover,
.nav-menu a.active {
    color: #667eea;
    border-bottom-color: #667eea;
}
.hamburger {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 5px;
}
.hamburger span {
    display: block;
    width: 25px;
    height: 3px;
    background: #333;
    border-radius: 3px;
    transition: 0.3s;
}

/* 英雄区 */
.hero {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    text-align: center;
    padding: 100px 20px;
    clip-path: polygon(0 0, 100% 0, 100% 85%, 0 100%);
}
.hero h1 {
    font-size: 3rem;
    margin-bottom: 20px;
}
.hero p {
    font-size: 1.2rem;
    opacity: 0.9;
    margin-bottom: 30px;
}

/* 按钮 */
.btn-primary {
    display: inline-block;
    padding: 12px 30px;
    background: white;
    color: #667eea;
    border-radius: 50px;
    font-weight: 600;
    transition: transform 0.3s, box-shadow 0.3s;
    border: none;
    cursor: pointer;
}
.btn-primary:hover {
    transform: translateY(-3px);
    box-shadow: 0 10px 20px rgba(0,0,0,0.2);
}
.btn-secondary {
    display: inline-block;
    padding: 10px 25px;
    background: transparent;
    color: #667eea;
    border: 2px solid #667eea;
    border-radius: 50px;
    font-weight: 600;
    transition: 0.3s;
    cursor: pointer;
}
.btn-secondary:hover {
    background: #667eea;
    color: white;
}

/* 功能卡片 */
.features {
    padding: 80px 0;
}
.section-title {
    text-align: center;
    font-size: 2rem;
    margin-bottom: 50px;
    color: #333;
}
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 30px;
    padding: 0 20px;
}
.card {
    background: white;
    border-radius: 20px;
    padding: 40px 20px;
    text-align: center;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
    cursor: pointer;
    transition: transform 0.3s, box-shadow 0.3s;
    animation: fadeInUp 0.6s ease;
}
.card:hover {
    transform: translateY(-10px);
    box-shadow: 0 20px 40px rgba(0,0,0,0.15);
}
.card i {
    font-size: 2.5rem;
    color: #667eea;
    margin-bottom: 20px;
}
.card h3 {
    margin-bottom: 10px;
}

/* 每日一句预览 */
.daily-preview {
    padding: 60px 20px;
    background: white;
}
.daily-card {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
    border-radius: 20px;
    padding: 40px;
    text-align: center;
    max-width: 600px;
    margin: 0 auto;
}
.daily-card .en {
    font-size: 1.5rem;
    margin-bottom: 10px;
}
.daily-card .cn {
    font-size: 1.2rem;
    opacity: 0.9;
    margin-bottom: 15px;
}
.daily-card .analysis {
    font-size: 1rem;
    opacity: 0.8;
}

/* 页面通用 */
.page-hero {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
    text-align: center;
    padding: 60px 20px;
}
.page-hero h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
}

/* 闪卡 */
.flashcard-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 60px 20px;
}
.flashcard {
    width: 300px;
    height: 200px;
    perspective: 1000px;
    cursor: pointer;
    margin-bottom: 30px;
}
.card-inner {
    width: 100%;
    height: 100%;
    transition: transform 0.6s;
    transform-style: preserve-3d;
    position: relative;
}
.flashcard.flipped .card-inner {
    transform: rotateY(180deg);
}
.card-front, .card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 20px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.8rem;
    font-weight: 600;
    box-shadow: 0 10px 30px rgba(0,0,0,0.2);
}
.card-front {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
}
.card-back {
    background: white;
    color: #333;
    transform: rotateY(180deg);
}
.card-controls {
    display: flex;
    gap: 20px;
}
.card-controls button {
    padding: 10px 20px;
    border: none;
    border-radius: 10px;
    background: white;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    cursor: pointer;
    transition: 0.3s;
    font-size: 1.2rem;
}
.card-controls button:hover {
    transform: scale(1.1);
}

/* 每日一句列表 */
.daily-list {
    padding: 40px 20px;
}
.daily-item {
    background: white;
    border-radius: 15px;
    padding: 25px;
    margin-bottom: 20px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.08);
    animation: fadeInUp 0.5s ease;
}
.daily-item .en {
    font-size: 1.3rem;
    font-weight: 600;
    margin-bottom: 5px;
}
.daily-item .cn {
    color: #666;
    margin-bottom: 10px;
}
.daily-item .analysis {
    color: #999;
    font-size: 0.9rem;
}

/* 语法练习 */
.quiz-container {
    padding: 60px 20px;
    max-width: 600px;
    margin: 0 auto;
}
#quiz {
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
}
#question {
    font-size: 1.3rem;
    margin-bottom: 25px;
}
#options {
    display: flex;
    flex-direction: column;
    gap: 12px;
    margin-bottom: 25px;
}
.option {
    padding: 12px 20px;
    border: 2px solid #e0e0e0;
    border-radius: 12px;
    cursor: pointer;
    transition: 0.3s;
}
.option:hover {
    border-color: #667eea;
    background: #f0f0ff;
}
.option.selected {
    border-color: #667eea;
    background: #e8e8ff;
}
#feedback {
    margin-top: 20px;
    font-weight: 600;
}

/* 听力训练 */
.listening-container {
    padding: 60px 20px;
    max-width: 600px;
    margin: 0 auto;
}
.audio-player {
    margin-bottom: 30px;
}
.audio-player audio {
    width: 100%;
}
.dictation textarea {
    width: 100%;
    height: 150px;
    padding: 15px;
    border-radius: 15px;
    border: 2px solid #e0e0e0;
    font-size: 1rem;
    margin-bottom: 20px;
    resize: vertical;
}

/* 口语跟读 */
.speaking-container {
    padding: 60px 20px;
    max-width: 600px;
    margin: 0 auto;
    text-align: center;
}
.sentence-card {
    background: white;
    border-radius: 20px;
    padding: 30px;
    margin-bottom: 30px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
}
#target-sentence {
    font-size: 1.5rem;
    margin-bottom: 20px;
}
.record-area {
    display: flex;
    gap: 15px;
    justify-content: center;
    flex-wrap: wrap;
    margin-bottom: 30px;
}
#score-area {
    font-size: 1.3rem;
}
#score {
    font-weight: 700;
    color: #667eea;
}

/* 学习报告 */
.report-container {
    padding: 60px 20px;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 30px;
}
.stat-card {
    background: white;
    border-radius: 20px;
    padding: 30px;
    text-align: center;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
    animation: fadeInUp 0.6s ease;
}
.stat-card h3 {
    margin-bottom: 15px;
    color: #666;
}
.stat-card p {
    font-size: 2rem;
    font-weight: 700;
    color: #667eea;
}

/* 课程库 */
.courses-container {
    padding: 60px 20px;
}
.category-section {
    margin-bottom: 50px;
}
.category-section h2 {
    font-size: 1.8rem;
    margin-bottom: 25px;
    color: #333;
}
.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 25px;
}
.course-card {
    background: white;
    border-radius: 20px;
    overflow: hidden;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
    transition: transform 0.3s;
}
.course-card:hover {
    transform: translateY(-5px);
}
.video-wrapper video {
    width: 100%;
    display: block;
}
.article-wrapper {
    padding: 25px;
}
.article-wrapper h3 {
    margin-bottom: 10px;
}
.article-wrapper p {
    color: #666;
    margin-bottom: 15px;
}

/* 管理后台 */
.admin-login {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: linear-gradient(135deg, #667eea, #764ba2);
}
.login-box {
    background: white;
    padding: 50px;
    border-radius: 20px;
    box-shadow: 0 20px 40px rgba(0,0,0,0.2);
    width: 400px;
    max-width: 90%;
}
.login-box h1 {
    text-align: center;
    margin-bottom: 30px;
    color: #333;
}
.login-box input {
    width: 100%;
    padding: 12px 15px;
    margin-bottom: 20px;
    border: 2px solid #e0e0e0;
    border-radius: 10px;
    font-size: 1rem;
}
.login-box .error {
    color: red;
    margin-bottom: 15px;
    text-align: center;
}
.admin-container {
    max-width: 800px;
    margin: 50px auto;
    padding: 30px;
    background: white;
    border-radius: 20px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.1);
}
.admin-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 20px;
    margin: 30px 0;
}
.admin-card {
    background: #f0f0ff;
    padding: 20px;
    border-radius: 15px;
    text-align: center;
    font-weight: 600;
}

/* 页脚 */
footer {
    background: #333;
    color: white;
    text-align: center;
    padding: 30px 20px;
    margin-top: 60px;
}

/* 动画 */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* 响应式 */
@media (max-width: 768px) {
    .nav-menu {
        display: none;
        flex-direction: column;
        position: absolute;
        top: 70px;
        left: 0;
        width: 100%;
        background: white;
        box-shadow: 0 10px 20px rgba(0,0,0,0.1);
        padding: 20px;
    }
    .nav-menu.active {
        display: flex;
    }
    .hamburger {
        display: flex;
    }
    .hero h1 {
        font-size: 2rem;
    }
    .card-grid {
        grid-template-columns: 1fr;
    }
    .flashcard {
        width: 250px;
        height: 170px;
    }
}
```

```javascript