:root {
    /* Colors */
    --bg-dark: #0a0a12;
    --bg-card: #161622;
    --text-primary: #ffffff;
    --text-secondary: #a0a0b0;
    --accent-primary: #6c5ce7;
    --accent-secondary: #00cec9;
    --accent-gradient: linear-gradient(135deg, #6c5ce7, #00cec9);
    --glass-border: rgba(255, 255, 255, 0.1);

    /* Typography */
    --font-heading: 'Space Grotesk', sans-serif;
    --font-body: 'Outfit', sans-serif;

    /* Spacing */
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 2rem;
    --spacing-xl: 4rem;

    /* Transitions */
    --transition-fast: 0.3s ease;
}

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

body {
    font-family: var(--font-body);
    background-color: var(--bg-dark);
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
}

.app-container {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.main-header {
    padding: var(--spacing-md) var(--spacing-lg);
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: rgba(10, 10, 18, 0.8);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--glass-border);
    position: sticky;
    top: 0;
    z-index: 100;
}

.logo {
    font-family: var(--font-heading);
    font-size: 1.5rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    cursor: pointer;
}

.highlight {
    color: var(--accent-secondary);
}

.main-nav {
    display: flex;
    gap: var(--spacing-md);
}

.lang-switcher {
    display: flex;
    gap: var(--spacing-sm);
    margin-left: var(--spacing-md);
}

.lang-btn {
    background: transparent;
    border: 1px solid var(--glass-border);
    color: var(--text-secondary);
    padding: 4px 8px;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.8rem;
    transition: var(--transition-fast);
}

.lang-btn:hover,
.lang-btn.active {
    background: var(--accent-primary);
    color: white;
    border-color: var(--accent-primary);
}

.nav-btn {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    font-family: var(--font-body);
    font-weight: 500;
    cursor: pointer;
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: 8px;
    transition: var(--transition-fast);
}

.nav-btn:hover,
.nav-btn.active {
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.05);
}

/* Main Content */
.content-area {
    flex: 1;
    padding: var(--spacing-xl) var(--spacing-lg);
    max-width: 1200px;
    margin: 0 auto;
    width: 100%;
}

.page-section {
    display: none;
    animation: fadeIn 0.5s ease;
}

.page-section.active {
    display: block;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Hero Section */
.hero {
    text-align: center;
    margin-bottom: var(--spacing-xl);
}

.hero h1 {
    font-family: var(--font-heading);
    font-size: 4rem;
    line-height: 1.1;
    margin-bottom: var(--spacing-md);
}

.gradient-text {
    background: var(--accent-gradient);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-lg);
}

.cta-btn {
    background: var(--accent-gradient);
    border: none;
    color: white;
    padding: 1rem 2rem;
    font-size: 1.1rem;
    border-radius: 50px;
    cursor: pointer;
    font-weight: 600;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.cta-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 20px rgba(108, 92, 231, 0.3);
}

/* Subject Tabs */
.subject-tabs {
    margin-top: var(--spacing-xl);
}

.tab-nav {
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
    margin-bottom: var(--spacing-lg);
    border-bottom: 2px solid var(--glass-border);
    padding-bottom: var(--spacing-sm);
}

.tab-btn {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    padding: var(--spacing-md) var(--spacing-lg);
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition-fast);
    position: relative;
}

.tab-btn::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 0;
    right: 0;
    height: 3px;
    background: var(--accent-gradient);
    transform: scaleX(0);
    transition: transform var(--transition-fast);
}

.tab-btn.active {
    color: var(--text-primary);
}

.tab-btn.active::after {
    transform: scaleX(1);
}

.tab-btn:hover {
    color: var(--text-primary);
}

.tab-content {
    position: relative;
    min-height: 300px;
}

.tab-pane {
    display: none;
}

.tab-pane.active {
    display: block;
    animation: fadeIn 0.5s ease;
}

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

.feature-card {
    background: var(--bg-card);
    border: 1px solid var(--glass-border);
    padding: var(--spacing-lg);
    border-radius: 16px;
    cursor: pointer;
    transition: var(--transition-fast);
}

.feature-card:hover {
    border-color: var(--accent-primary);
    transform: translateY(-5px);
}

.card-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.feature-card h3 {
    font-family: var(--font-heading);
    margin-bottom: var(--spacing-sm);
    font-size: 1.5rem;
}

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

/* Demos */
.demo-header {
    text-align: center;
    margin-bottom: var(--spacing-lg);
}

.demo-container {
    background: var(--bg-card);
    border-radius: 20px;
    padding: var(--spacing-lg);
    display: flex;
    flex-direction: column;
    align-items: center;
    border: 1px solid var(--glass-border);
    box-shadow: 0 20px 50px rgba(0, 0, 0, 0.3);
}

canvas {
    background: #0f0f1a;
    border-radius: 12px;
    margin-bottom: var(--spacing-md);
    max-width: 100%;
    box-shadow: inset 0 0 20px rgba(0, 0, 0, 0.5);
}

.controls {
    display: flex;
    gap: var(--spacing-lg);
    align-items: center;
    margin-top: var(--spacing-md);
    flex-wrap: wrap;
    justify-content: center;
}

.action-btn {
    padding: 0.8rem 1.5rem;
    border-radius: 8px;
    border: none;
    cursor: pointer;
    font-weight: 600;
    background: var(--accent-primary);
    color: white;
    transition: var(--transition-fast);
}

.action-btn.secondary {
    background: rgba(255, 255, 255, 0.1);
}

.action-btn:hover {
    opacity: 0.9;
}

/* Footer */
.main-footer {
    text-align: center;
    padding: var(--spacing-lg);
    color: var(--text-secondary);
    border-top: 1px solid var(--glass-border);
    margin-top: auto;
}