:root {
    --bg-dark: #0a0a0f;
    --bg-card: #12121a;
    --bg-card-hover: #16161f;
    --border: #2a2a3a;

    --text-primary: #f0f0f5;
    --text-secondary: #8b8b9e;
    --text-muted: #5a5a6e;

    --accent-blue: #3b82f6;
    --accent-orange: #f59e0b;
    --accent-green: #10b981;
    --accent-purple: #8b5cf6;
    --accent-pink: #ec4899;

    --font-sans: 'Inter', -apple-system, sans-serif;
    --font-mono: 'JetBrains Mono', monospace;
}

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

body {
    background: var(--bg-dark);
    font-family: var(--font-sans);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
}

/* Header */
.header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 32px;
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    background: var(--bg-dark);
    z-index: 100;
}

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
    font-weight: 600;
    font-size: 18px;
}

.logo-icon {
    width: 32px;
    height: 32px;
    background: var(--accent-blue);
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn-icon {
    width: 40px;
    height: 40px;
    border-radius: 10px;
    border: 1px solid var(--border);
    background: transparent;
    color: var(--text-secondary);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s;
}

.btn-icon:hover {
    border-color: var(--text-secondary);
    color: var(--text-primary);
}

/* Main */
.main {
    max-width: 900px;
    margin: 0 auto;
    padding: 48px 24px;
}

/* Welcome section */
.welcome {
    text-align: center;
    margin-bottom: 48px;
}

.welcome-greeting {
    font-size: 14px;
    text-transform: uppercase;
    letter-spacing: 2px;
    color: var(--text-muted);
    margin-bottom: 12px;
}

.welcome-name {
    font-size: 42px;
    font-weight: 700;
    margin-bottom: 8px;
    background: linear-gradient(135deg, var(--text-primary) 0%, var(--text-secondary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.welcome-subtitle {
    font-size: 16px;
    color: var(--text-secondary);
}

/* Stats row */
.stats-row {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 16px;
    margin-bottom: 48px;
}

.stat-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 16px;
    padding: 20px 24px;
    text-align: center;
}

.stat-value {
    font-family: var(--font-mono);
    font-size: 32px;
    font-weight: 600;
    margin-bottom: 4px;
}

.stat-value.blue {
    color: var(--accent-blue);
}

.stat-value.green {
    color: var(--accent-green);
}

.stat-value.orange {
    color: var(--accent-orange);
}

.stat-label {
    font-size: 13px;
    color: var(--text-secondary);
}

/* Tips section */
.tips {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    padding: 28px 32px;
    margin-bottom: 48px;
}

.tips-header {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 20px;
}

.tips-icon {
    width: 36px;
    height: 36px;
    background: rgba(245, 158, 11, 0.15);
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 18px;
}

.tips-title {
    font-size: 16px;
    font-weight: 600;
    margin: 0;
}

.tips-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.tip-item {
    display: flex;
    align-items: flex-start;
    gap: 12px;
    font-size: 15px;
    color: var(--text-secondary);
    line-height: 1.5;
}

.tip-icon {
    flex-shrink: 0;
    width: 24px;
    height: 24px;
    background: var(--bg-dark);
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 12px;
    margin-top: 2px;
}

/* Section header */
.section-header-front {
    font-weight: bold;
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 20px;
}

.section-title-front {
    font-weight: bold;
    font-size: 13px;
    text-transform: uppercase;
    letter-spacing: 1.5px;
    color: var(--text-muted);
}

.section-link {
    font-size: 14px;
    color: var(--accent-blue);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 4px;
    transition: opacity 0.2s;
}

.section-link:hover {
    opacity: 0.8;
}

/* Subject cards */
.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
    gap: 20px;
    margin-bottom: 48px;
}

.subject-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    padding: 28px;
    cursor: pointer;
    position: relative;
    overflow: hidden;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.subject-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: var(--card-accent);
    opacity: 0;
    transition: opacity 0.3s;
}

.subject-card:hover {
    transform: translateY(-4px);
    border-color: var(--card-accent);
    box-shadow: 0 20px 40px -20px var(--card-glow);
}

.subject-card:hover::before {
    opacity: 1;
}

.subject-card.math {
    --card-accent: var(--accent-blue);
    --card-glow: rgba(59, 130, 246, 0.3);
}

.subject-card.physics {
    --card-accent: var(--accent-purple);
    --card-glow: rgba(139, 92, 246, 0.3);
}

.subject-card.chemistry {
    --card-accent: var(--accent-green);
    --card-glow: rgba(16, 185, 129, 0.3);
}

.subject-icon {
    width: 56px;
    height: 56px;
    border-radius: 14px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 20px;
    font-size: 28px;
    background: linear-gradient(135deg, var(--card-accent) 0%, transparent 100%);
    opacity: 0.9;
}

.subject-visual {
    height: 80px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 20px;
}

.math-visual {
    font-family: var(--font-mono);
    font-size: 36px;
    font-weight: 500;
    color: var(--accent-blue);
    opacity: 0.9;
}

.math-visual sup {
    font-size: 20px;
}

.subject-name {
    font-size: 20px;
    font-weight: 600;
    margin-bottom: 6px;
}

.subject-meta {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-top: 16px;
    padding-top: 16px;
    border-top: 1px solid var(--border);
}

.meta-item {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 13px;
    color: var(--text-secondary);
}

.meta-dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background: var(--card-accent);
}

.progress-mini {
    flex: 1;
    height: 4px;
    background: var(--border);
    border-radius: 2px;
    overflow: hidden;
}

.progress-mini-fill {
    height: 100%;
    background: var(--card-accent);
    border-radius: 2px;
}

/* Continue section */
.continue-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    padding: 24px 28px;
    display: flex;
    align-items: center;
    gap: 20px;
    cursor: pointer;
    transition: all 0.2s;
}

.continue-card:hover {
    border-color: var(--accent-blue);
    background: var(--bg-card-hover);
}

.continue-icon {
    width: 48px;
    height: 48px;
    background: rgba(59, 130, 246, 0.15);
    border: 1px solid rgba(59, 130, 246, 0.3);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--accent-blue);
    flex-shrink: 0;
}

.continue-content {
    flex: 1;
}

.continue-label {
    font-size: 12px;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--text-muted);
    margin-bottom: 4px;
}

.continue-title {
    font-size: 16px;
    font-weight: 500;
    margin-bottom: 2px;
}

.continue-subtitle {
    font-size: 14px;
    color: var(--text-secondary);
}

.continue-arrow {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: var(--accent-blue);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    flex-shrink: 0;
    transition: transform 0.2s;
}

.continue-card:hover .continue-arrow {
    transform: translateX(4px);
}

/* Course badge */
.course-badge {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 8px 14px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    font-size: 13px;
    color: var(--text-secondary);
    margin-top: 16px;
}

.course-badge strong {
    color: var(--text-primary);
    font-weight: 500;
}

/* Notes */
.notes {
    max-width: 900px;
    margin: 60px auto 0;
    padding: 32px;
    background: rgba(59, 130, 246, 0.05);
    border: 1px solid rgba(59, 130, 246, 0.2);
    border-radius: 16px;
}

.notes h3 {
    font-size: 16px;
    color: var(--accent-blue);
    margin-bottom: 20px;
}

.notes-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 32px;
}

.notes-column h4 {
    font-size: 13px;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--text-secondary);
    margin-bottom: 12px;
}

.notes ul {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.notes li {
    font-size: 14px;
    color: var(--text-secondary);
    padding-left: 20px;
    position: relative;
    line-height: 1.5;
}

.notes li::before {
    content: '→';
    position: absolute;
    left: 0;
    color: var(--accent-blue);
}

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

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

.welcome {
    animation: fadeInUp 0.5s ease backwards;
}

.stats-row {
    animation: fadeInUp 0.5s ease 0.1s backwards;
}

.tips {
    animation: fadeInUp 0.5s ease 0.2s backwards;
}

.subjects-grid {
    animation: fadeInUp 0.5s ease 0.3s backwards;
}

@media (max-width: 640px) {
    .stats-row {
        grid-template-columns: 1fr;
    }

    .subjects-grid {
        grid-template-columns: 1fr;
    }

    .notes-grid {
        grid-template-columns: 1fr;
    }

    .welcome-name {
        font-size: 32px;
    }
}