:root {
    --bg-color: #000000;
    --text-primary: #ffffff;
    --text-secondary: #a1a1aa;
    --card-bg: rgba(255, 255, 255, 0.04);
    --card-border: rgba(255, 255, 255, 0.08);
    --card-hover: rgba(255, 255, 255, 0.08);
}

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

body {
    background-color: var(--bg-color);
    color: var(--text-primary);
    font-family: "SF Pro Display", -apple-system, BlinkMacSystemFont, "Inter", "Helvetica Neue", Helvetica, Arial, sans-serif;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

a {
    color: var(--text-primary);
    text-decoration: none;
    transition: opacity 0.2s ease;
}

a:hover {
    opacity: 0.7;
}

/* Header & Nav */
header {
    padding: 2rem 5%;
    display: flex;
    justify-content: space-between;
    align-items: center;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--card-border);
    position: sticky;
    top: 0;
    z-index: 100;
}

.logo {
    font-size: 1.25rem;
    font-weight: 600;
    letter-spacing: -0.02em;
}

nav {
    display: flex;
    gap: 1.5rem;
    align-items: center;
}

.nav-link {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

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

.lang-toggle {
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    color: var(--text-primary);
    padding: 0.25rem 0.75rem;
    border-radius: 999px;
    font-size: 0.8rem;
    cursor: pointer;
    transition: all 0.2s;
}

.lang-toggle:hover {
    background: var(--card-hover);
}

/* Main Content */
main {
    flex: 1;
    max-width: 800px;
    margin: 0 auto;
    padding: 4rem 2rem;
    width: 100%;
}

.hero {
    text-align: center;
    margin-bottom: 5rem;
    animation: fadeIn 1s ease-out;
}

.app-icon-placeholder {
    width: 120px;
    height: 120px;
    background: linear-gradient(135deg, #2a2a2a, #111111);
    border-radius: 28px;
    margin: 0 auto 2rem;
    border: 1px solid var(--card-border);
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 20px 40px rgba(0,0,0,0.5);
}

h1 {
    font-size: 3.5rem;
    font-weight: 700;
    letter-spacing: -0.04em;
    margin-bottom: 1rem;
    line-height: 1.1;
}

.subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: 2.5rem;
    font-weight: 400;
}

.download-btn {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    background-color: var(--text-primary);
    color: var(--bg-color);
    padding: 0.875rem 2rem;
    border-radius: 999px;
    font-weight: 600;
    font-size: 1.1rem;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.download-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 20px rgba(255,255,255,0.1);
    opacity: 1;
}

/* Features Grid */
.features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
    margin-top: 4rem;
}

.feature-card {
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    padding: 2.5rem;
    border-radius: 24px;
    transition: transform 0.3s ease, background 0.3s ease;
}

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

.feature-card h3 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    font-weight: 600;
}

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

/* Content Pages (Privacy, Support) */
.page-title {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.last-updated {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 3rem;
}

.content-section {
    margin-bottom: 3rem;
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    padding: 2.5rem;
    border-radius: 24px;
}

.content-section h2 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    border-bottom: 1px solid var(--card-border);
    padding-bottom: 0.5rem;
}

.content-section p {
    color: var(--text-secondary);
    margin-bottom: 1rem;
}

.content-section ul {
    color: var(--text-secondary);
    margin-left: 1.5rem;
    margin-bottom: 1rem;
}

.content-section li {
    margin-bottom: 0.5rem;
}

/* FAQ */
.faq-item {
    margin-bottom: 1.5rem;
}

.faq-item h3 {
    font-size: 1.1rem;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

/* Footer */
footer {
    padding: 3rem 5%;
    text-align: center;
    border-top: 1px solid var(--card-border);
    margin-top: auto;
}

.footer-links {
    display: flex;
    justify-content: center;
    gap: 2rem;
    margin-bottom: 1.5rem;
}

.copyright {
    color: var(--text-secondary);
    font-size: 0.8rem;
}

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Utility classes for language switching */
.lang-en { display: none; }
.show-en .lang-en { display: block; }
.show-en .lang-zh { display: none; }
.show-en .lang-zh-inline { display: none; }
.show-en .lang-en-inline { display: inline; }
.lang-en-inline { display: none; }

@media (max-width: 768px) {
    h1 { font-size: 2.5rem; }
    .hero { margin-bottom: 3rem; }
    .features { grid-template-columns: 1fr; }
    main { padding: 2rem 1.5rem; }
}