:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #f8fafc;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --bg-color: #ffffff;
    --bg-alt: #f1f5f9;
    --header-height: 80px;
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
}

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

body {
    font-family: var(--font-family);
    color: var(--text-main);
    background-color: var(--bg-color);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

html[lang="en"] .lang-zh { display: none !important; }
html[lang="zh"] .lang-en { display: none !important; }

/* Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 1rem;
    color: var(--text-main);
}

p {
    margin-bottom: 1rem;
    color: var(--text-muted);
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.3s ease;
}

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

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

/* Header & Navigation */
header {
    background-color: var(--bg-color);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 1000;
    height: var(--header-height);
    display: flex;
    align-items: center;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    width: 100%;
}

.logo {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary-color);
    letter-spacing: -0.5px;
}

nav ul {
    list-style: none;
    display: flex;
    gap: 30px;
    align-items: center;
}

nav ul li a {
    color: var(--text-main);
    font-weight: 500;
    font-size: 1rem;
}

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

.lang-toggle-btn {
    background-color: var(--bg-alt);
    border: 1px solid var(--border-color);
    padding: 8px 16px;
    border-radius: 20px;
    cursor: pointer;
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-main);
    transition: all 0.3s ease;
}

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

/* Hero Section */
.hero {
    padding: 120px 0;
    background-color: var(--bg-alt);
    text-align: center;
}

.hero h1 {
    font-size: 3.5rem;
    margin-bottom: 20px;
    max-width: 800px;
    margin-left: auto;
    margin-right: auto;
}

.hero p {
    font-size: 1.25rem;
    max-width: 600px;
    margin: 0 auto 40px auto;
}

.btn {
    display: inline-block;
    padding: 12px 32px;
    background-color: var(--primary-color);
    color: white;
    font-weight: 600;
    border-radius: 6px;
    font-size: 1.1rem;
    border: none;
    cursor: pointer;
    transition: background-color 0.3s ease, transform 0.2s ease;
}

.btn:hover {
    background-color: var(--primary-hover);
    color: white;
    transform: translateY(-2px);
}

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

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

/* Sections */
.section {
    padding: 80px 0;
}

.section-title {
    text-align: center;
    font-size: 2.5rem;
    margin-bottom: 50px;
}

/* Features/Services Grid */
.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
}

.card {
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 40px 30px;
    transition: box-shadow 0.3s ease, transform 0.3s ease;
}

.card:hover {
    box-shadow: 0 10px 25px rgba(0,0,0,0.05);
    transform: translateY(-5px);
}

.card-icon {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: 20px;
}

.card h3 {
    font-size: 1.5rem;
    margin-bottom: 15px;
}

/* Page Headers */
.page-header {
    background-color: var(--primary-color);
    color: white;
    padding: 80px 0;
    text-align: center;
}

.page-header h1 {
    color: white;
    font-size: 3rem;
    margin-bottom: 0;
}

/* Content Pages (Privacy, Terms, About) */
.content-page {
    max-width: 800px;
    margin: 0 auto;
    padding: 60px 20px;
}

.content-page h2 {
    margin-top: 40px;
    font-size: 1.75rem;
}

.content-page h3 {
    margin-top: 25px;
    font-size: 1.25rem;
}

.content-page p, .content-page li {
    font-size: 1.1rem;
    line-height: 1.8;
    margin-bottom: 20px;
}

.content-page ul, .content-page ol {
    margin-bottom: 20px;
    padding-left: 20px;
}

.content-page li {
    margin-bottom: 10px;
}

/* Contact Section */
.contact-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 50px;
}

.contact-info-item {
    margin-bottom: 30px;
}

.contact-info-item h4 {
    margin-bottom: 10px;
    font-size: 1.2rem;
}

.contact-form {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.form-group label {
    font-weight: 600;
}

.form-group input, .form-group textarea {
    padding: 12px 15px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-family: inherit;
    font-size: 1rem;
}

.form-group input:focus, .form-group textarea:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

/* Footer */
footer {
    background-color: var(--text-main);
    color: var(--bg-alt);
    padding: 60px 0 30px 0;
}

.footer-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 40px;
    margin-bottom: 40px;
}

.footer-col h4 {
    color: white;
    margin-bottom: 20px;
    font-size: 1.2rem;
}

.footer-col ul {
    list-style: none;
}

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

.footer-col ul li a {
    color: var(--text-muted);
}

.footer-col ul li a:hover {
    color: white;
}

.footer-bottom {
    border-top: 1px solid rgba(255,255,255,0.1);
    padding-top: 30px;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* Responsive */
@media (max-width: 768px) {
    nav ul {
        display: none; /* In a real app, we'd add a hamburger menu. Keeping it simple for static. */
    }
    
    .hero h1 {
        font-size: 2.5rem;
    }
    
    .contact-grid {
        grid-template-columns: 1fr;
    }
}