:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #0ea5e9;
    --bg-color: #f8fafc;
    --surface-color: #ffffff;
    --text-main: #0f172a;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --radius-md: 8px;
    --radius-lg: 12px;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

/* Language Toggle Logic */
html[lang="en"] .lang-zh { display: none !important; }
html[lang="zh"] .lang-en { display: none !important; }

/* Layout & Container */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 24px;
}

/* Header & Nav */
header {
    background-color: var(--surface-color);
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 72px;
}

.logo {
    font-size: 24px;
    font-weight: 700;
    color: var(--primary-color);
    text-decoration: none;
    letter-spacing: -0.5px;
}

.nav-links {
    display: flex;
    gap: 32px;
    align-items: center;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-muted);
    font-weight: 500;
    transition: color 0.2s ease;
}

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

.lang-switch {
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    padding: 6px 12px;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-weight: 500;
    color: var(--text-main);
    transition: all 0.2s ease;
}

.lang-switch:hover {
    background: var(--border-color);
}

/* Hero Section */
.hero {
    padding: 120px 0;
    background: linear-gradient(135deg, #eff6ff 0%, #e0f2fe 100%);
    text-align: center;
}

.hero h1 {
    font-size: 56px;
    font-weight: 800;
    color: var(--text-main);
    margin-bottom: 24px;
    letter-spacing: -1px;
    line-height: 1.2;
}

.hero p {
    font-size: 20px;
    color: var(--text-muted);
    max-width: 700px;
    margin: 0 auto 40px;
}

.btn {
    display: inline-block;
    padding: 14px 28px;
    border-radius: var(--radius-md);
    font-weight: 600;
    text-decoration: none;
    transition: all 0.2s ease;
}

.btn-primary {
    background-color: var(--primary-color);
    color: white;
    box-shadow: var(--shadow-md);
}

.btn-primary:hover {
    background-color: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-lg);
}

.btn-secondary {
    background-color: white;
    color: var(--text-main);
    border: 1px solid var(--border-color);
    margin-left: 16px;
}

.btn-secondary:hover {
    background-color: var(--bg-color);
}

/* Sections */
.section {
    padding: 96px 0;
}

.section-title {
    text-align: center;
    font-size: 36px;
    font-weight: 700;
    margin-bottom: 16px;
}

.section-subtitle {
    text-align: center;
    color: var(--text-muted);
    font-size: 18px;
    margin-bottom: 64px;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

/* Grid Layouts */
.grid-3 {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 32px;
}

.grid-2 {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 48px;
    align-items: center;
}

/* Cards */
.card {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    padding: 32px;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border-color);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.card-icon {
    width: 48px;
    height: 48px;
    background: #eff6ff;
    color: var(--primary-color);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 24px;
    font-size: 24px;
}

.card h3 {
    font-size: 20px;
    margin-bottom: 12px;
}

.card p {
    color: var(--text-muted);
}

/* Document Pages (Privacy, Terms, About) */
.doc-header {
    background-color: var(--surface-color);
    padding: 64px 0;
    border-bottom: 1px solid var(--border-color);
}

.doc-header h1 {
    font-size: 40px;
    margin-bottom: 16px;
}

.doc-content {
    background: var(--surface-color);
    padding: 64px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    margin-top: -32px;
    margin-bottom: 96px;
    border: 1px solid var(--border-color);
}

.doc-content h2 {
    font-size: 24px;
    margin: 40px 0 16px;
    color: var(--text-main);
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border-color);
}

.doc-content h3 {
    font-size: 20px;
    margin: 24px 0 12px;
}

.doc-content p {
    margin-bottom: 16px;
    color: #334155;
}

.doc-content ul {
    margin-bottom: 16px;
    padding-left: 24px;
    color: #334155;
}

.doc-content li {
    margin-bottom: 8px;
}

.contact-info-box {
    background: #f8fafc;
    border-left: 4px solid var(--primary-color);
    padding: 24px;
    border-radius: 0 var(--radius-md) var(--radius-md) 0;
    margin: 32px 0;
}

.contact-info-box p {
    margin-bottom: 8px;
}

.contact-info-box p:last-child {
    margin-bottom: 0;
}

/* Footer */
footer {
    background-color: #0f172a;
    color: #94a3b8;
    padding: 64px 0 32px;
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1fr;
    gap: 48px;
    margin-bottom: 48px;
}

.footer-brand h2 {
    color: white;
    font-size: 24px;
    margin-bottom: 16px;
}

.footer-title {
    color: white;
    font-weight: 600;
    margin-bottom: 24px;
    text-transform: uppercase;
    font-size: 14px;
    letter-spacing: 1px;
}

.footer-links {
    list-style: none;
}

.footer-links li {
    margin-bottom: 12px;
}

.footer-links a {
    color: #94a3b8;
    text-decoration: none;
    transition: color 0.2s ease;
}

.footer-links a:hover {
    color: white;
}

.footer-bottom {
    text-align: center;
    padding-top: 32px;
    border-top: 1px solid #1e293b;
    font-size: 14px;
}

/* Responsive */
@media (max-width: 992px) {
    .grid-3 { grid-template-columns: repeat(2, 1fr); }
    .footer-grid { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 768px) {
    .grid-2, .grid-3 { grid-template-columns: 1fr; }
    .nav-links { display: none; }
    .hero h1 { font-size: 40px; }
    .doc-content { padding: 32px; }
    .footer-grid { grid-template-columns: 1fr; }
}