:root {
    /* Colors */
    --color-bg: #0f172a;
    --color-surface: #1e293b;
    --color-primary: #3b82f6;
    --color-primary-hover: #2563eb;
    --color-secondary: #8b5cf6;
    --color-accent: #f43f5e;
    --color-text: #f1f5f9;
    --color-text-muted: #94a3b8;
    --color-success: #10b981;
    --color-error: #ef4444;

    /* Typography */
    --font-main: 'Inter', sans-serif;
    --font-display: 'Outfit', sans-serif;

    /* Spacing & Layout */
    --container-width: 1200px;
    --header-height: 70px;
    --radius-md: 12px;
    --radius-lg: 24px;

    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-medium: 0.3s ease;
}

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

body {
    background-color: var(--color-bg);
    color: var(--color-text);
    font-family: var(--font-main);
    line-height: 1.6;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

a {
    text-decoration: none;
    color: inherit;
    transition: var(--transition-fast);
}

ul {
    list-style: none;
}

/* Header */
.main-header {
    height: var(--header-height);
    background: rgba(15, 23, 42, 0.8);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 2rem;
    position: sticky;
    top: 0;
    z-index: 100;
}

.logo-text {
    font-family: var(--font-display);
    font-weight: 900;
    font-size: 1.5rem;
    letter-spacing: -0.5px;
}

.highlight {
    color: var(--color-primary);
}

.main-nav ul {
    display: flex;
    gap: 2rem;
}

.main-nav a {
    font-weight: 600;
    font-size: 0.95rem;
    color: var(--color-text-muted);
}

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

.lang-switch {
    display: flex;
    gap: 0.5rem;
}

.lang-btn {
    background: transparent;
    border: 1px solid rgba(255, 255, 255, 0.1);
    color: var(--color-text-muted);
    padding: 4px 8px;
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.8rem;
    transition: var(--transition-fast);
}

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

/* Main Content */
main#app {
    flex: 1;
    width: 100%;
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 2rem;
}

/* Hero Section */
.hero {
    min-height: 60vh;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    flex-direction: column;
    padding: 4rem 0;
}

.hero h1 {
    font-family: var(--font-display);
    font-size: 4rem;
    line-height: 1.1;
    margin-bottom: 1.5rem;
    background: linear-gradient(135deg, #fff 0%, var(--color-placeholder, #94a3b8) 100%);
    /* Fallback or simple gradient */
    background: linear-gradient(to right, #fff, var(--color-primary));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hero p {
    font-size: 1.25rem;
    color: var(--color-text-muted);
    max-width: 600px;
    margin: 0 auto 3rem auto;
}

/* CTA Button */
.cta-button {
    display: inline-block;
    background: var(--color-primary);
    color: white;
    padding: 1rem 2.5rem;
    border-radius: 50px;
    font-weight: 700;
    font-size: 1.1rem;
    box-shadow: 0 4px 14px 0 rgba(59, 130, 246, 0.39);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.cta-button:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(59, 130, 246, 0.23);
    background: var(--color-primary-hover);
}

/* Features Grid */
.features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    margin-top: 4rem;
}

.feature-card {
    background: var(--color-surface);
    padding: 2rem;
    border-radius: var(--radius-md);
    border: 1px solid rgba(255, 255, 255, 0.05);
    transition: transform var(--transition-medium);
}

.feature-card:hover {
    transform: translateY(-5px);
    border-color: rgba(255, 255, 255, 0.1);
}

.feature-card h3 {
    margin-bottom: 0.5rem;
    font-family: var(--font-display);
    color: var(--color-secondary);
}

.feature-card p {
    color: var(--color-text-muted);
    font-size: 0.95rem;
}

/* Footer */
.main-footer {
    padding: 2rem;
    text-align: center;
    border-top: 1px solid rgba(255, 255, 255, 0.05);
    margin-top: auto;
    color: var(--color-text-muted);
    font-size: 0.9rem;
}

/* Responsive */
@media (max-width: 768px) {
    .hero h1 {
        font-size: 2.5rem;
    }

    .main-header {
        padding: 0 1rem;
    }

    .main-nav {
        display: none;
        /* Mobile menu todo: hamburger */
    }
}

/* Quiz Appendix */
.quiz-container {
    max-width: 800px;
    margin: 0 auto;
    background: var(--color-surface);
    padding: 2rem;
    border-radius: var(--radius-lg);
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
    animation: fadeIn 0.5s ease;
}

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

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

.title {
    margin-bottom: 2rem;
    text-align: center;
}

.options-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 1rem;
    margin-top: 0.5rem;
    margin-bottom: 2rem;
}

.option-btn {
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid rgba(255, 255, 255, 0.1);
    color: var(--color-text);
    padding: 1rem;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition-medium);
}

.option-btn:hover {
    background: rgba(255, 255, 255, 0.1);
}

.option-btn.selected {
    background: var(--color-primary);
    border-color: var(--color-primary);
    color: white;
}

/* Question Area */
.quiz-header {
    margin-bottom: 1.5rem;
}

.timer-bar {
    width: 100%;
    height: 6px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 10px;
    overflow: hidden;
    margin-bottom: 0.5rem;
}

.timer-fill {
    height: 100%;
    background: var(--color-primary);
    width: 100%;
    transition: width 1s linear;
}

.stats {
    display: flex;
    justify-content: space-between;
    font-size: 0.9rem;
    color: var(--color-text-muted);
}

.question-card h2 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    line-height: 1.4;
    min-height: 60px;
}

/* Answers */
.answers-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1rem;
}

.answer-btn {
    background: transparent;
    border: 2px solid rgba(255, 255, 255, 0.1);
    color: var(--color-text);
    padding: 1rem;
    border-radius: var(--radius-md);
    text-align: left;
    font-size: 1.05rem;
    cursor: pointer;
    transition: var(--transition-fast);
}

.answer-btn:hover:not(:disabled) {
    border-color: var(--color-primary);
    background: rgba(59, 130, 246, 0.1);
}

.answer-btn:disabled {
    cursor: not-allowed;
    opacity: 0.7;
}

.answer-btn.correct {
    background: rgba(16, 185, 129, 0.2) !important;
    border-color: var(--color-success) !important;
    color: var(--color-success) !important;
}

.answer-btn.wrong {
    background: rgba(239, 68, 68, 0.2) !important;
    border-color: var(--color-error) !important;
    color: var(--color-error) !important;
}

/* Feedback */
.feedback-area {
    margin-top: 2rem;
    padding-top: 1rem;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    animation: slideDown 0.3s ease;
}

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

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

.feedback-message {
    font-weight: 800;
    font-size: 1.2rem;
    margin-bottom: 0.5rem;
}

.feedback-message.success {
    color: var(--color-success);
}

.feedback-message.error {
    color: var(--color-error);
}

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

.info-link {
    display: inline-block;
    color: var(--color-primary);
    text-decoration: none;
    font-weight: 600;
    margin-right: 1rem;
    margin-top: 0.5rem;
    border-bottom: 1px dashed var(--color-primary);
}

.info-link:hover {
    border-bottom-style: solid;
}

#next-btn {
    display: block;
    margin-top: 2rem;
    /* More spacing */
    width: 100%;
    /* Make it full width for better mobile tap */
}

.hidden {
    display: none !important;
}

.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

.secondary {
    background: transparent;
    border: 1px solid var(--color-primary);
    color: var(--color-primary);
}

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

.score-circle {
    font-size: 3rem;
    font-weight: 900;
    margin: 2rem 0;
    color: var(--color-primary);
    font-family: var(--font-display);
}

/* Videos */
.video-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    margin-top: 2rem;
}

.video-card {
    background: var(--color-surface);
    border-radius: var(--radius-md);
    overflow: hidden;
    transition: transform var(--transition-medium);
}

.video-card:hover {
    transform: translateY(-5px);
}

.video-embed {
    width: 100%;
    aspect-ratio: 9/16;
    background: #000;
    position: relative;
    cursor: pointer;
}

.video-embed img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    opacity: 0.8;
    transition: opacity 0.3s;
}

.video-embed:hover img {
    opacity: 0.6;
}

.play-btn {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background: var(--color-primary);
    color: white;
    border: none;
    width: 60px;
    height: 60px;
    border-radius: 50%;
    font-size: 24px;
    cursor: pointer;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.3);
    display: flex;
    align-items: center;
    justify-content: center;
    transition: transform 0.2s, box-shadow 0.2s;
}

.video-embed:hover .play-btn {
    transform: translate(-50%, -50%) scale(1.1);
    box-shadow: 0 6px 20px rgba(0, 0, 0, 0.4);
}

.video-info {
    padding: 1rem;
}

.video-title {
    font-weight: 600;
    margin-bottom: 0.5rem;
    line-height: 1.3;
}

.link-btn {
    display: inline-block;
    margin-top: 0.5rem;
    color: var(--color-primary);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.9rem;
}

.link-btn:hover {
    text-decoration: underline;
}

.info-section {
    max-width: 800px;
    margin: 0 auto 3rem;
    padding: 2rem;
    background: var(--color-surface);
    border-radius: var(--radius-md);
}

.info-section h2 {
    margin-bottom: 1rem;
    font-family: var(--font-display);
    color: var(--color-primary);
}