/* --- 全局与基础样式 --- */
:root {
    --primary-color: #007bff;
    --primary-color-dark: #0056b3;
    --secondary-color: #f8f9fa;
    --text-color: #333;
    --light-gray-color: #e9ecef;
    --white-color: #fff;
    --shadow: 0 4px 6px rgba(0,0,0,0.1);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--white-color);
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 20px;
}

/* --- 通用组件 --- */
.btn {
    display: inline-block;
    padding: 10px 20px;
    border: none;
    border-radius: 5px;
    text-decoration: none;
    color: var(--white-color);
    background-color: var(--primary-color);
    transition: background-color 0.3s ease;
    cursor: pointer;
}

.btn:hover {
    background-color: var(--primary-color-dark);
}

.btn-primary {
    background-color: transparent;
    border: 1px solid var(--primary-color);
    color: var(--primary-color);
}

.btn-primary:hover {
    background-color: var(--primary-color);
    color: var(--white-color);
}

.btn-large {
    padding: 15px 30px;
    font-size: 1.1em;
}

.section-title {
    text-align: center;
    font-size: 2.2em;
    margin-bottom: 50px;
    color: var(--text-color);
}

/* --- 导航栏 --- */
.navbar {
    background: var(--white-color);
    box-shadow: var(--shadow);
    padding: 12px 0;
    position: sticky;
    top: 0;
    z-index: 1000;
}

.navbar .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.2em;
    font-weight: bold;
    color: var(--primary-color);
    text-decoration: none;
}

.nav-links {
    list-style: none;
    display: flex;
}

.nav-links li {
    margin-left: 25px;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-color);
    font-weight: 500;
    transition: color 0.3s ease;
}

.nav-links a:hover {
    color: var(--primary-color);
}

/* --- 英雄区域 --- */
.hero {
    background: linear-gradient(rgba(0, 123, 255, 0.05), rgba(0, 123, 255, 0.05));
    padding: 100px 0;
    text-align: center;
}

.hero h1 {
    font-size: 2.5em;
    max-width: 800px;
    margin: 0 auto 20px;
}

.hero .subtitle {
    font-size: 1.2em;
    max-width: 700px;
    margin: 0 auto 30px;
    color: #555;
}

/* --- 英雄区模块按钮样式 --- */
.hero-modules {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 15px;
    margin-top: 30px;
}

.module-btn {
    min-width: 140px;
    margin: 0 5px 10px 5px;
    font-size: 1em;
    background-color: var(--primary-color);
    color: var(--white-color);
    border-radius: 30px;
    box-shadow: 0 2px 6px rgba(0,123,255,0.08);
    transition: background 0.2s, color 0.2s, transform 0.2s;
}
.module-btn:hover {
    background-color: var(--primary-color-dark);
    color: var(--white-color);
    transform: translateY(-2px);
}

/* --- 各个区块通用样式 --- */
.features-section, .modules-section, .cta-section {
    padding: 80px 0;
}

/* --- 核心功能 --- */
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 30px;
}

.feature-card {
    background: var(--white-color);
    padding: 30px;
    border-radius: 8px;
    text-align: center;
    box-shadow: var(--shadow);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.feature-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 15px rgba(0,0,0,0.15);
}

.feature-icon {
    font-size: 3em;
    margin-bottom: 15px;
}

.feature-card h3 {
    margin-bottom: 10px;
    font-size: 1.3em;
}

/* --- 学习模块 --- */
.modules-section {
     background-color: var(--secondary-color);
}
.modules-grid {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 15px;
}

.module-card {
    background: var(--white-color);
    color: var(--primary-color);
    padding: 15px 25px;
    border-radius: 50px;
    font-weight: 500;
    box-shadow: 0 2px 4px rgba(0,0,0,0.08);
    transition: all 0.3s ease;
}
.module-card:hover {
    background: var(--primary-color);
    color: var(--white-color);
    transform: translateY(-3px);
}

/* --- CTA --- */
.cta-section {
    background-color: var(--primary-color);
    color: var(--white-color);
    text-align: center;
}

.cta-section h2 {
    font-size: 2em;
    margin-bottom: 15px;
}
.cta-section p {
    margin-bottom: 25px;
    font-size: 1.1em;
}
.cta-section .btn {
    background-color: var(--white-color);
    color: var(--primary-color);
    font-weight: bold;
}
.cta-section .btn:hover {
    background-color: var(--light-gray-color);
}

/* --- 页脚 --- */
.footer {
    background-color: var(--text-color);
    color: var(--white-color);
    text-align: center;
    padding: 30px 0;
}

/* --- 响应式设计 --- */
@media (max-width: 768px) {
    .nav-links {
        display: none; /* 在移动端简单隐藏，可以后续用JS实现汉堡菜单 */
    }

    .hero h1 {
        font-size: 2em;
    }

    .hero .subtitle {
        font-size: 1em;
    }

    .section-title {
        font-size: 1.8em;
    }

    .features-grid {
        grid-template-columns: 1fr;
    }
    
    .hero-modules {
        gap: 10px;
    }
    .module-btn {
        min-width: 100px;
        font-size: 0.95em;
        padding: 10px 12px;
    }
}