/* CSS 变量定义 */
:root {
    /* 亮色模式变量 */
    --bg-color: #ffffff;
    --text-color: #333333;
    --header-bg: #f8f9fa;
    --card-bg: #ffffff;
    --card-border: #eaeaea;
    --primary-color: #0056b3;
    --hover-color: #004494;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
}

[data-theme="dark"] {
    /* 暗色模式变量 */
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --header-bg: #1e1e1e;
    --card-bg: #1e1e1e;
    --card-border: #333333;
    --primary-color: #4da3ff;
    --hover-color: #80bdff;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* 头部与导航 */
.header {
    position: sticky;
    top: 0;
    background-color: var(--header-bg);
    box-shadow: var(--shadow);
    z-index: 1000;
    transition: background-color 0.3s ease;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 70px;
}

.logo {
    font-size: 1.5rem;
    font-weight: bold;
    color: var(--primary-color);
    text-decoration: none;
}

.nav-menu {
    display: flex;
    gap: 30px;
}

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

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

.nav-link.active::after {
    content: '';
    position: absolute;
    bottom: -5px;
    left: 0;
    width: 100%;
    height: 2px;
    background-color: var(--primary-color);
}

.nav-actions {
    display: flex;
    align-items: center;
    gap: 15px;
}

/* 主题切换按钮 */
.theme-toggle {
    background: none;
    border: none;
    cursor: pointer;
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 5px;
}

.icon-sun, .icon-moon {
    display: none;
}

[data-theme="light"] .icon-moon { display: block; }
[data-theme="dark"] .icon-sun { display: block; }

/* 汉堡菜单 */
.hamburger {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 5px;
}

.hamburger span {
    width: 25px;
    height: 3px;
    background-color: var(--text-color);
    border-radius: 3px;
    transition: all 0.3s ease;
}

.hamburger.active span:nth-child(1) {
    transform: translateY(8px) rotate(45deg);
}
.hamburger.active span:nth-child(2) {
    opacity: 0;
}
.hamburger.active span:nth-child(3) {
    transform: translateY(-8px) rotate(-45deg);
}

/* 主体内容 */
.section {
    padding: 80px 0;
    min-height: 60vh;
}

.hero {
    display: flex;
    align-items: center;
    text-align: center;
    min-height: 80vh;
    background-color: var(--header-bg);
}

.hero h1 {
    font-size: 3rem;
    margin-bottom: 20px;
}

.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 20px;
    margin-top: 40px;
}

.card {
    background-color: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: 8px;
    padding: 30px;
    box-shadow: var(--shadow);
    transition: transform 0.3s ease, background-color 0.3s ease;
}

.card:hover {
    transform: translateY(-5px);
}

.card h3 {
    margin-bottom: 15px;
    color: var(--primary-color);
}

/* 底部 */
.footer {
    background-color: var(--header-bg);
    text-align: center;
    padding: 20px 0;
    border-top: 1px solid var(--card-border);
}

/* 响应式设计 (移动端) */
@media (max-width: 768px) {
    .hamburger {
        display: flex;
    }

    .nav-menu {
        position: absolute;
        top: 70px;
        left: 0;
        width: 100%;
        background-color: var(--header-bg);
        flex-direction: column;
        align-items: center;
        gap: 0;
        max-height: 0;
        overflow: hidden;
        transition: max-height 0.3s ease-in-out;
        box-shadow: var(--shadow);
    }

    .nav-menu.active {
        max-height: 300px;
    }

    .nav-link {
        padding: 15px 0;
        width: 100%;
        text-align: center;
        border-bottom: 1px solid var(--card-border);
    }

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