/* 全局重置 & 设计变量 */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
:root {
    --brand-primary: #1a73e8;
    --brand-secondary: #0b1a2f;
    --accent: #ffb347;
    --glass-bg: rgba(255,255,255,0.08);
    --glass-border: rgba(255,255,255,0.15);
    --shadow-card: 0 12px 30px rgba(0,0,0,0.08);
    --radius-card: 24px;
    --radius-sm: 12px;
    --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --font-sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
    --bg-body: #f8faff;
    --text-main: #1e293b;
    --text-light: #475569;
    --card-bg: #ffffff;
    --footer-bg: #0b1a2f;
    --footer-text: #cbd5e1;
}
body.dark-mode {
    --bg-body: #0f172a;
    --text-main: #e2e8f0;
    --text-light: #94a3b8;
    --card-bg: #1e293b;
    --shadow-card: 0 12px 30px rgba(0,0,0,0.4);
    --glass-bg: rgba(0,0,0,0.25);
    --glass-border: rgba(255,255,255,0.05);
}
html { scroll-behavior: smooth; }
body {
    font-family: var(--font-sans);
    background: var(--bg-body);
    color: var(--text-main);
    line-height: 1.6;
    transition: background var(--transition), color var(--transition);
    -webkit-font-smoothing: antialiased;
}
.container { max-width: 1280px; margin: 0 auto; padding: 0 24px; }
/* 玻璃效果卡片 */
.glass-card {
    background: var(--glass-bg);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-card);
    box-shadow: var(--shadow-card);
}
/* 渐变banner */
.gradient-bg {
    background: linear-gradient(135deg, #0b1a2f 0%, #1a73e8 70%, #3b8aff 100%);
    color: white;
}
.section-title { font-size: 2.2rem; font-weight: 700; letter-spacing: -0.01em; margin-bottom: 1.2rem; }
.section-subtitle { font-size: 1.1rem; color: var(--text-light); max-width: 720px; }
.btn-primary {
    display: inline-block; background: var(--brand-primary); color: #fff;
    padding: 0.9rem 2.5rem; border-radius: 60px; font-weight: 600;
    transition: all var(--transition); border: none; cursor: pointer;
    box-shadow: 0 6px 20px rgba(26,115,232,0.25);
}
.btn-primary:hover { background: #1557b0; transform: translateY(-3px); box-shadow: 0 12px 28px rgba(26,115,232,0.35); }
/* 吸顶导航 */
.header { position: sticky; top: 0; z-index: 100; background: rgba(255,255,255,0.7); backdrop-filter: blur(16px); -webkit-backdrop-filter: blur(16px); border-bottom: 1px solid rgba(0,0,0,0.02); transition: background var(--transition); }
.dark-mode .header { background: rgba(15,23,42,0.8); border-bottom: 1px solid rgba(255,255,255,0.05); }
.header-inner { display: flex; align-items: center; justify-content: space-between; padding: 0.8rem 0; }
.logo svg { height: 40px; width: auto; display: block; }
.nav-list { display: flex; gap: 2rem; list-style: none; align-items: center; }
.nav-list a { text-decoration: none; color: var(--text-main); font-weight: 500; font-size: 0.95rem; transition: color var(--transition); position: relative; }
.nav-list a::after { content: ''; position: absolute; bottom: -4px; left: 0; width: 0; height: 2px; background: var(--brand-primary); transition: width var(--transition); }
.nav-list a:hover::after, .nav-list a.active::after { width: 100%; }
.nav-list a.active { color: var(--brand-primary); }
.dark-toggle { background: none; border: none; font-size: 1.4rem; cursor: pointer; padding: 0 0.5rem; color: var(--text-main); }
.mobile-menu-btn { display: none; background: none; border: none; font-size: 2rem; cursor: pointer; color: var(--text-main); }
@media (max-width: 900px) {
    .nav-list { display: none; flex-direction: column; background: var(--card-bg); position: absolute; top: 100%; left: 0; right: 0; padding: 1.5rem; gap: 1.2rem; border-radius: 0 0 24px 24px; box-shadow: var(--shadow-card); }
    .nav-list.open { display: flex; }
    .mobile-menu-btn { display: block; }
}
/* Hero 轮播 */
.hero-carousel { position: relative; overflow: hidden; border-radius: 0 0 40px 40px; }
.hero-slide { display: none; padding: 5rem 0 6rem; min-height: 70vh; align-items: center; }
.hero-slide.active { display: flex; }
.hero-content { flex: 1; }
.hero-title { font-size: 3.2rem; font-weight: 800; line-height: 1.2; margin-bottom: 1.5rem; }
.hero-desc { font-size: 1.2rem; opacity: 0.9; margin-bottom: 2rem; max-width: 600px; }
.hero-actions { display: flex; gap: 1rem; flex-wrap: wrap; }
.hero-indicators { position: absolute; bottom: 2rem; left: 50%; transform: translateX(-50%); display: flex; gap: 0.75rem; }
.hero-indicators button { width: 14px; height: 14px; border-radius: 50%; border: 2px solid white; background: transparent; cursor: pointer; transition: background var(--transition); }
.hero-indicators button.active { background: white; }
/* 卡片网格 */
.grid-3 { display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 2rem; margin: 2rem 0; }
.card { background: var(--card-bg); border-radius: var(--radius-card); padding: 2rem; box-shadow: var(--shadow-card); transition: transform var(--transition), box-shadow var(--transition); }
.card:hover { transform: translateY(-6px); box-shadow: 0 20px 40px rgba(0,0,0,0.08); }
.dark-mode .card:hover { box-shadow: 0 20px 40px rgba(0,0,0,0.3); }
.icon-box svg { width: 48px; height: 48px; stroke: var(--brand-primary); fill: none; stroke-width: 1.5; }
/* 数字动画 */
.stat-number { font-size: 2.8rem; font-weight: 700; color: var(--brand-primary); }
/* 折叠FAQ */
.faq-item { border-bottom: 1px solid rgba(0,0,0,0.06); padding: 1rem 0; }
.faq-question { display: flex; justify-content: space-between; font-weight: 600; cursor: pointer; font-size: 1.1rem; background: none; border: none; width: 100%; text-align: left; color: var(--text-main); padding: 0.5rem 0; }
.faq-answer { max-height: 0; overflow: hidden; transition: max-height 0.35s ease; padding-left: 0.5rem; color: var(--text-light); }
.faq-item.open .faq-answer { max-height: 300px; padding-top: 0.6rem; }
/* 文章卡片 */
.article-list { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 2rem; margin: 2rem 0; }
.article-card { background: var(--card-bg); border-radius: var(--radius-card); padding: 1.5rem; box-shadow: var(--shadow-card); }
.article-meta { font-size: 0.85rem; color: var(--text-light); margin: 0.5rem 0; }
/* footer */
.footer { background: var(--footer-bg); color: var(--footer-text); padding: 3rem 0 1.5rem; border-radius: 48px 48px 0 0; margin-top: 4rem; }
.footer a { color: #94a3b8; text-decoration: none; }
.footer-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(170px, 1fr)); gap: 2rem; }
/* 滚动动画 */
.fade-up { opacity: 0; transform: translateY(30px); transition: opacity 0.7s ease, transform 0.7s ease; }
.fade-up.visible { opacity: 1; transform: translateY(0); }
/* 返回顶部 */
#backToTop { position: fixed; bottom: 2rem; right: 2rem; width: 48px; height: 48px; border-radius: 50%; background: var(--brand-primary); color: white; border: none; font-size: 1.5rem; cursor: pointer; box-shadow: 0 8px 20px rgba(0,0,0,0.15); display: none; z-index: 99; }
/* 响应式 */
@media (max-width: 640px) {
    .hero-title { font-size: 2.2rem; }
    .section-title { font-size: 1.8rem; }
}