/* 基础样式和变量 */
:root {
    /* 苹果风格颜色系统 */
    --primary-blue: #764BA2;
    --primary-blue-dark: #3f1767;
    --secondary-gray: #8E8E93;
    --background-primary: #FFFFFF;
    --background-secondary: #F2F2F7;
    --background-tertiary: #FFFFFF;
    --text-primary: #000000;
    --text-secondary: #3C3C43;
    --text-tertiary: #8E8E93;
    --border-color: #C6C6C8;
    --highlight-gradient: linear-gradient(135deg, #764BA2 0%, #3f1767 100%);
    
    /* 间距系统 */
    --spacing-xs: 4px;
    --spacing-sm: 8px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    --spacing-xxl: 48px;
    --spacing-xxxl: 64px;
    
    /* 圆角 */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    
    /* 阴影 */
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1), 0 1px 2px rgba(0, 0, 0, 0.06);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07), 0 2px 4px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1), 0 4px 6px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.1), 0 10px 10px rgba(0, 0, 0, 0.04);
    
    /* 字体 */
    --font-family: 'SF Pro Display', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
}

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

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

body {
    font-family: var(--font-family);
    color: var(--text-primary);
    background-color: var(--background-primary);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* 导航栏 */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: #764ba2;
    backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border-color);
    z-index: 1000;
    padding: 10px 0;
}

.nav-container {
    max-width: 1500px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.nav-brand {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-weight: 600;
    font-size: 1.25rem;
}

.logo-icon {
    width: 24px;
    height: 24px;
    color: var(--primary-blue);
}

.logo-text {
    background: var(--highlight-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: var(--spacing-xl);
}

.nav-link {
    text-decoration: none;
    color: white;
    font-weight: 400;
    transition: color 0.2s ease;
}

.nav-link:hover {
    color: var(--primary-blue);
}

.nav-actions {
    display: flex;
    gap: var(--spacing-md);
}

/* 英雄区域 */
.hero {
    padding: calc(var(--spacing-xxxl) + 60px) 0 var(--spacing-xxxl);
    background: linear-gradient(135deg, #FAFAFA 0%, #F0F0F5 100%);
    overflow: hidden;
}

.hero-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-xxxl);
    align-items: center;
}

.hero-content {
    z-index: 2;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 500;
    line-height: 1.2;
    margin-bottom: var(--spacing-lg);
    color: var(--text-primary);
    letter-spacing: 2px;
}

.highlight {
    background: var(--highlight-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-xl);
    line-height: 1.6;
}

.hero-actions {
    display: flex;
    gap: var(--spacing-md);
    flex-wrap: wrap;
}

.hero-visual {
    position: relative;
    display: flex;
    justify-content: center;
    align-items: center;
}

.hero-image {
    position: relative;
    border-radius: var(--radius-xl);
    overflow: hidden;
    box-shadow: var(--shadow-xl);
    transform: perspective(1000px) rotateY(-5deg) rotateX(5deg);
    transition: transform 0.3s ease;
}

.hero-image:hover {
    transform: perspective(1000px) rotateY(-2deg) rotateX(2deg);
}

.main-image {
    width: 100%;
    height: auto;
    max-width: 500px;
    display: block;
}

/* 特色功能 */
.features {
    padding: var(--spacing-xxxl) 0;
    background: var(--background-primary);
}

.features-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

.section-title {
    font-size: 2.5rem;
    font-weight: 500;
    text-align: center;
    margin-bottom: 20px;
    color: var(--text-primary);
    letter-spacing: 2px;
}

.section-subtitle {
    font-size: 1.28rem;
    color: var(--text-secondary);
    text-align: center;
    margin-bottom: var(--spacing-xxl);
    max-width: 1088px;
    margin-left: auto;
    margin-right: auto;
    letter-spacing: 1.2px;
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-xl);
}

.feature-card {
    background: var(--background-primary);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    text-align: center;
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
}

.feature-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
    border-color: var(--primary-blue);
}

.feature-icon {
    width: 60px;
    height: 60px;
    margin: 0 auto var(--spacing-lg);
    background: linear-gradient(135deg, var(--primary-blue) 0%,var(--primary-blue) 100%);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
}

.feature-icon svg {
    width: 28px;
    height: 28px;
}

.feature-title {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.feature-description {
    color: var(--text-secondary);
    line-height: 1.6;
}

/* 课程区域 */
.courses {
    padding: var(--spacing-xxxl) 0;
    background: var(--background-secondary);
}

.courses-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-xl);
}

/* 统计数据 */
.stats {
    padding: var(--spacing-xxxl) 0;
    background: #764ba2;
    color: white;
}

.stats-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-xl);
}

.stat-item {
    text-align: center;
}

.stat-number {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: var(--spacing-sm);
    background: linear-gradient(135deg, #FFD60A 0%, #FF9500 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-label {
    font-size: 1.125rem;
    opacity: 0.8;
}

/* 页脚 */
.footer {
    background: var(--background-secondary);
    padding: var(--spacing-xxl) 0 var(--spacing-lg);
}

.footer-container {
    max-width: 1500px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

.footer-content {
    display: grid;
    grid-template-columns: 1fr 2fr;
    gap: var(--spacing-xxl);
    margin-bottom: var(--spacing-xl);
}

.footer-brand {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-weight: 600;
    font-size: 1.25rem;
}

.footer-links {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-xl);
}

.footer-section h4 {
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: var(--spacing-sm);
}

.footer-section ul li a {
    color: var(--text-secondary);
    text-decoration: none;
    transition: color 0.2s ease;
}

.footer-section ul li a:hover {
    color: var(--primary-blue);
}

.footer-bottom {
    border-top: 1px solid var(--border-color);
    padding: 24px 0;
    text-align: center;
    font-size: 14px;
    color: var(--text-secondary);
}

/* ------------------------- */
/* Animations                */
/* ------------------------- */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in-up {
    animation: fadeIn 0.8s ease forwards;
}

.logo {
    width: auto;
    height: 18px;
}

/* 用户菜单样式 */
.user-menu {
    position: relative;
    display: flex;
    align-items: center;
}

.user-info {
    display: flex;
    align-items: normal;
    gap: var(--spacing-sm);
    padding: 8px 12px;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all 0.2s ease;
    border: 1px solid transparent;
    flex-direction: column;
}

.user-info:hover {
    background: var(--background-secondary);
    border-color: var(--primary-blue);
}

.user-avatar {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    object-fit: cover;
    border: 2px solid var(--primary-blue);
}

.user-name {
    font-weight: 500;
    color: var(--text-primary);
    max-width: 120px;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.dropdown-icon {
    transition: transform 0.2s ease;
    color: var(--text-secondary);
}

.user-info:hover .dropdown-icon {
    transform: rotate(180deg);
}

.user-dropdown {
    position: absolute;
    top: 100%;
    right: 0;
    background: var(--background-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    min-width: 200px;
    z-index: 1000;
    margin-top: 8px;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-10px);
    transition: all 0.2s ease;
}

.user-dropdown.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.dropdown-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: 12px 16px;
    text-decoration: none;
    color: var(--text-primary);
    transition: background-color 0.2s ease;
    border: none;
    background: none;
    width: 100%;
    text-align: left;
    cursor: pointer;
    font-size: 0.875rem;
}

.dropdown-item:hover {
    background: var(--background-secondary);
}

.dropdown-item svg {
    width: 16px;
    height: 16px;
    color: var(--text-secondary);
}

.dropdown-divider {
    height: 1px;
    background: var(--border-color);
    margin: 8px 0;
}

/* 认证表单样式 */
.auth-form {
    max-width: 400px;
    margin: 0 auto;
}

.auth-title {
    font-size: 1.5rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.auth-subtitle {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-xl);
    font-size: 0.875rem;
}

.auth-form-content {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.auth-links {
    text-align: center;
    margin-top: var(--spacing-md);
}

.auth-links a {
    color: var(--primary-blue);
    text-decoration: none;
    font-size: 0.875rem;
}

.auth-links a:hover {
    text-decoration: underline;
}

.auth-switch {
    text-align: center;
    margin-top: var(--spacing-lg);
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.auth-switch a {
    color: var(--primary-blue);
    text-decoration: none;
    font-weight: 500;
}

.auth-switch a:hover {
    text-decoration: underline;
}

/* 密码强度指示器 */
.password-strength {
    margin-top: var(--spacing-sm);
}

.password-strength-bar {
    height: 4px;
    background: var(--background-secondary);
    border-radius: 2px;
    overflow: hidden;
    margin-bottom: var(--spacing-xs);
}

.strength-indicator {
    height: 100%;
    transition: all 0.3s ease;
    border-radius: 2px;
}

.strength-weak .strength-indicator {
    background: #F44336;
    width: 33%;
}

.strength-medium .strength-indicator {
    background: #FF9800;
    width: 66%;
}

.strength-strong .strength-indicator {
    background: #4CAF50;
    width: 100%;
}

.strength-text {
    font-size: 0.75rem;
    font-weight: 500;
}

.strength-weak {
    color: #F44336;
}

.strength-medium {
    color: #FF9800;
}

.strength-strong {
    color: #4CAF50;
}

/* 平板端适配 */
@media (max-width: 1024px) and (min-width: 769px) {
    .nav-container {
        padding: 0 var(--spacing-lg);
    }
    
    .hero-container {
        gap: var(--spacing-xxl);
        padding: 0 var(--spacing-lg);
    }
    
    .hero-title {
        font-size: 3rem;
    }
    
    .features-container,
    .courses-container {
        padding: 0 var(--spacing-lg);
    }
    
    .features-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-xxl);
    }
    
    .courses-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-xxl);
    }
}

/* 手机端适配 */
@media (max-width: 768px) {
    /* 导航栏移动端适配 */
    .nav-container {
        padding: 0 var(--spacing-md);
    }
    
    .nav-menu {
        display: none; /* 在移动端隐藏导航菜单 */
    }
    
    .nav-actions {
        gap: var(--spacing-sm);
    }
    
    .nav-actions .btn-secondary,
    .nav-actions .btn-primary {
        padding: 8px 16px;
        font-size: 0.875rem;
        border-radius: 8px;
        min-height: 44px; /* 确保触摸目标足够大 */
        display: flex;
        align-items: center;
        justify-content: center;
        touch-action: manipulation;
        -webkit-tap-highlight-color: transparent;
    }
    
    /* 英雄区域移动端适配 */
    .hero-container {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
        text-align: center;
        padding: 0 var(--spacing-md);
    }
    
    .hero-title {
        font-size: 2.5rem;
        line-height: 1.1;
    }
    
    .hero-subtitle {
        font-size: 1.125rem;
    }
    
    .hero-actions {
        justify-content: center;
        gap: var(--spacing-sm);
    }
    
    .hero-actions .btn-primary-large,
    .hero-actions .btn-secondary-large {
        padding: 12px 24px;
        font-size: 1rem;
        min-height: 48px;
        touch-action: manipulation;
        -webkit-tap-highlight-color: transparent;
    }
    
    /* 特色功能区域移动端适配 */
    .features-container {
        padding: 0 var(--spacing-md);
    }
    
    .features-grid {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }
    
    /* 课程展示区域移动端适配 */
    .courses-container {
        padding: 0 var(--spacing-md);
    }
    
    .courses-grid {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }
    
    /* 统计数据区域移动端适配 */
    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-lg);
    }
    
    /* 页脚移动端适配 */
    .footer-container {
        padding: 0 var(--spacing-md);
    }
    
    .footer-content {
        flex-direction: column;
        gap: var(--spacing-xl);
        text-align: center;
    }
    
    .footer-links {
        flex-direction: column;
        gap: var(--spacing-lg);
    }
    
    /* 用户菜单移动端适配 */
    .user-name {
        display: none;
    }
    
    .user-dropdown {
        right: 0;
        left: auto;
        min-width: 180px;
    }
    
    /* 认证表单移动端适配 */
    .auth-form {
        max-width: 100%;
        padding: 0 var(--spacing-md);
    }
    
    /* 模态框移动端适配 */
    .modal-content {
        width: 95%;
        max-width: 95vw;
        margin: 0 auto;
    }
    
    .modal-header {
        padding: var(--spacing-md);
    }
    
    .modal-body {
        padding: var(--spacing-md);
    }
}