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

:root {
    --primary: #5B8DEF;
    --primary-dark: #4A7BD9;
    --text: #2D3748;
    --text-light: #718096;
    --bg: #FAFBFC;
    --card-bg: #FFFFFF;
    --border: #E2E8F0;
    --shadow: 0 4px 20px rgba(0,0,0,0.04);
    --radius: 16px;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.7;
    padding-top: 64px; /* 给固定导航栏留空间 */
}

/* ========== 导航栏 ========== */
nav {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background: rgba(255,255,255,0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border);
    z-index: 100;
    transition: box-shadow 0.3s;
}

.nav-container {
    max-width: 960px;
    margin: 0 auto;
    padding: 0 24px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 64px;
}

.logo {
    font-weight: 700;
    font-size: 1.25rem;
    color: var(--primary);
    text-decoration: none;
    letter-spacing: -0.5px;
}

.nav-links {
    display: flex;
    gap: 8px;
    list-style: none;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-light);
    font-size: 0.9rem;
    font-weight: 500;
    padding: 8px 16px;
    border-radius: 8px;
    transition: all 0.2s;
}

.nav-links a:hover {
    color: var(--primary);
    background: rgba(91, 141, 239, 0.08);
}

.nav-links a.active {
    color: var(--primary);
    background: rgba(91, 141, 239, 0.12);
    font-weight: 600;
}

/* ========== 内容区通用 ========== */
.container {
    max-width: 960px;
    margin: 0 auto;
    padding: 60px 24px;
}

.section-title {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 12px;
    text-align: center;
}

.section-desc {
    text-align: center;
    color: var(--text-light);
    margin-bottom: 40px;
    font-size: 1.05rem;
}

/* ========== 按钮 ========== */
.btn {
    display: inline-block;
    padding: 12px 28px;
    border-radius: 10px;
    font-weight: 600;
    text-decoration: none;
    transition: all 0.2s;
    border: none;
    cursor: pointer;
    font-size: 1rem;
}

.btn-primary {
    background: var(--primary);
    color: white;
    box-shadow: 0 4px 14px rgba(91, 141, 239, 0.35);
}

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(91, 141, 239, 0.45);
}

.btn-outline {
    background: transparent;
    color: var(--primary);
    border: 2px solid var(--primary);
}

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

/* ========== 卡片 ========== */
.card {
    background: var(--card-bg);
    border-radius: var(--radius);
    padding: 32px;
    border: 1px solid var(--border);
    box-shadow: var(--shadow);
}

/* ========== 页脚 ========== */
footer {
    text-align: center;
    padding: 40px 24px;
    color: var(--text-light);
    font-size: 0.9rem;
    border-top: 1px solid var(--border);
    margin-top: 40px;
}

/* ========== 淡入动画 ========== */
.fade-in {
    opacity: 0;
    transform: translateY(24px);
    transition: opacity 0.6s ease, transform 0.6s ease;
}
.fade-in.visible {
    opacity: 1;
    transform: translateY(0);
}

/* ========== 移动端适配 ========== */
@media (max-width: 640px) {
    .nav-links a {
        padding: 6px 10px;
        font-size: 0.85rem;
    }
    .section-title {
        font-size: 1.6rem;
    }
    .card {
        padding: 24px;
    }
}