:root {
    --bg: #f8fafc;
    --card: #ffffff;
    --text-primary: #111827;
    --text-secondary: #6b7280;
    --border: #e5e7eb;
    --blue: #2563eb;
    --green: #10b981;
    --yellow: #f59e0b;
    --red: #ef4444;
    --shadow: 0 20px 50px rgba(15, 23, 42, 0.08);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    font-family: 'Inter', sans-serif;
    color: var(--text-primary);
    background: linear-gradient(180deg, #f8fafc 0%, #edf2f7 100%);
}

.quiz-page-header {
    padding: 30px 24px 0;
}

.quiz-header-content {
    max-width: 1180px;
    margin: 0 auto;
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    gap: 20px;
}

.quiz-badge {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    background: rgba(37, 99, 235, 0.12);
    color: #1d4ed8;
    padding: 10px 16px;
    border-radius: 999px;
    font-weight: 700;
    letter-spacing: 0.02em;
    text-transform: uppercase;
    font-size: 0.85rem;
}

.quiz-page-header h1 {
    margin: 12px 0 8px;
    font-size: clamp(2rem, 3vw, 3rem);
    line-height: 1.05;
}

.quiz-subtitle {
    margin: 0;
    color: var(--text-secondary);
    max-width: 700px;
}

.quiz-links {
    display: flex;
    align-items: center;
    gap: 12px;
    flex-wrap: wrap;
}

.btn-link,
.btn-primary {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 14px 22px;
    border-radius: 999px;
    border: 1px solid transparent;
    text-decoration: none;
    font-weight: 700;
    transition: transform 0.2s ease, box-shadow 0.2s ease, background-color 0.2s ease;
}

.btn-link {
    color: var(--text-secondary);
    background: #ffffff;
    border-color: var(--border);
}

.btn-link:hover {
    transform: translateY(-2px);
    background: #f1f5f9;
}

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

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 18px 40px rgba(37, 99, 235, 0.18);
}

.quiz-main {
    display: flex;
    justify-content: center;
    padding: 40px 24px 60px;
}

.selection-screen,
.quiz-screen {
    width: min(980px, 100%);
}

.selection-card,
.quiz-card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 32px;
    padding: 38px;
    box-shadow: var(--shadow);
}

.selection-card h2 {
    margin: 0 0 12px;
    font-size: clamp(2rem, 2.4vw, 2.6rem);
    color: var(--text-primary);
}

.selection-card p {
    margin: 0 0 28px;
    color: var(--text-secondary);
    line-height: 1.7;
}

.chapter-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 18px;
}

.chapter-card {
    padding: 26px 22px;
    border-radius: 24px;
    border: 1px solid var(--border);
    background: #ffffff;
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 700;
    text-align: left;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.chapter-card span {
    display: block;
    margin-top: 8px;
    font-weight: 400;
    color: var(--text-secondary);
}

.chapter-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 22px 48px rgba(15, 23, 42, 0.08);
    border-color: #d1d5db;
}

.quiz-card-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 18px;
    margin-bottom: 32px;
}

.quiz-label {
    display: block;
    color: var(--text-secondary);
    margin-bottom: 8px;
}

.quiz-card-header strong {
    display: block;
    font-size: 1.5rem;
}

.quiz-info {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    align-items: center;
}

.quiz-timer {
    background: #f1f5f9;
    color: var(--text-primary);
    padding: 14px 20px;
    border-radius: 999px;
    font-weight: 700;
    letter-spacing: 0.01em;
}

.quiz-question-box {
    padding: 28px;
    border-radius: 28px;
    background: #f8fafc;
    border: 1px solid #e5e7eb;
    margin-bottom: 28px;
}

.quiz-question-box h2 {
    margin: 0 0 18px;
    font-size: clamp(1.8rem, 2.4vw, 2.4rem);
    line-height: 1.08;
}

.quiz-media {
    margin-top: 16px;
}

.quiz-media img {
    width: 100%;
    border-radius: 22px;
    display: block;
}

.options-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 18px;
}

.option-button {
    display: grid;
    grid-template-columns: 52px 1fr;
    gap: 14px;
    align-items: center;
    min-height: 130px;
    padding: 20px;
    border: none;
    border-radius: 26px;
    color: white;
    font-size: 1rem;
    font-weight: 700;
    cursor: pointer;
    transition: transform 0.25s ease, box-shadow 0.25s ease, opacity 0.25s ease;
    box-shadow: 0 18px 40px rgba(15, 23, 42, 0.12);
}

.option-button:hover:not(:disabled) {
    transform: translateY(-4px);
}

.option-button:disabled {
    opacity: 0.72;
    cursor: default;
}

.option-label {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 52px;
    height: 52px;
    border-radius: 18px;
    background: rgba(255,255,255,0.18);
    color: white;
    font-size: 1rem;
}

.option-0 {
    background: linear-gradient(135deg, var(--red), #fb7185);
}

.option-1 {
    background: linear-gradient(135deg, var(--blue), #60a5fa);
}

.option-2 {
    background: linear-gradient(135deg, var(--yellow), #fbbf24);
}

.option-3 {
    background: linear-gradient(135deg, var(--green), #34d399);
}

.option-button.correct {
    box-shadow: 0 0 0 4px rgba(16, 185, 129, 0.25);
}

.option-button.incorrect {
    box-shadow: 0 0 0 4px rgba(239, 68, 68, 0.25);
}

.quiz-actions-row {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    flex-wrap: wrap;
    margin-top: 28px;
}

.quiz-feedback {
    margin-top: 20px;
    padding: 18px 20px;
    border-radius: 22px;
    font-weight: 700;
    line-height: 1.5;
    border: 1px solid transparent;
    background: #f8fafc;
}

.quiz-feedback.correct {
    color: #065f46;
    border-color: rgba(16, 185, 129, 0.25);
    background: rgba(16, 185, 129, 0.08);
}

.quiz-feedback.incorrect {
    color: #b91c1c;
    border-color: rgba(239, 68, 68, 0.25);
    background: rgba(239, 68, 68, 0.08);
}

.btn-secondary,
.btn-next {
    border: none;
    border-radius: 999px;
    padding: 16px 24px;
    font-weight: 700;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease, opacity 0.2s ease;
}

.btn-secondary {
    background: #ffffff;
    color: var(--text-primary);
    border: 1px solid var(--border);
    box-shadow: 0 12px 30px rgba(15, 23, 42, 0.08);
}

.btn-secondary:hover {
    transform: translateY(-2px);
}

.btn-next {
    background: var(--blue);
    color: white;
}

.btn-next:hover:not(:disabled) {
    transform: translateY(-2px);
}

.hidden {
    display: none;
}

@media (max-width: 960px) {
    .chapter-grid,
    .options-grid {
        grid-template-columns: 1fr;
    }

    .quiz-card-header,
    .quiz-actions-row,
    .quiz-header-content {
        flex-direction: column;
        align-items: stretch;
    }
}

@media (max-width: 640px) {
    .quiz-page-header {
        padding-top: 20px;
    }

    .quiz-card,
    .selection-card {
        padding: 1.2rem;
        margin: 0.5rem;
    }

    .selection-card h2 {
        font-size: 1.5rem;
        margin-bottom: 0.8rem;
    }

    .selection-card p {
        font-size: 0.95rem;
        margin-bottom: 1.2rem;
    }

    .btn-link,
    .btn-primary,
    .btn-secondary,
    .btn-next {
        width: 100%;
        padding: 0.8rem 1rem;
        font-size: 0.95rem;
        min-height: 44px;
    }

    .chapter-card {
        padding: 1.2rem;
        min-height: 120px;
        font-size: 0.95rem;
    }

    .chapter-card span {
        font-size: 0.8rem;
    }

    .quiz-card-header {
        padding: 1rem;
        flex-direction: column;
        gap: 1rem;
    }

    .quiz-label {
        font-size: 0.85rem;
    }

    #chapterTitle,
    #questionCounter,
    #timerDisplay {
        font-size: 1.2rem;
    }
}

@media (max-width: 480px) {
    .quiz-main {
        padding: 0.5rem;
    }

    .quiz-card,
    .selection-card {
        padding: 1rem;
        margin: 0;
        border-radius: 12px;
    }

    .selection-card h2 {
        font-size: 1.3rem;
    }

    .selection-card p {
        font-size: 0.9rem;
    }

    .chapter-grid {
        grid-template-columns: 1fr;
        gap: 0.8rem;
    }

    .chapter-card {
        padding: 1rem;
        font-size: 0.9rem;
        min-height: 100px;
    }

    .quiz-question-box {
        margin: 1rem 0;
    }

    #questionText {
        font-size: 1.2rem;
        margin-bottom: 1rem;
    }

    .options-grid {
        gap: 0.8rem;
    }

    .quiz-option {
        padding: 0.8rem;
    }

    .btn-link,
    .btn-primary,
    .btn-secondary,
    .btn-next {
        padding: 1rem;
        font-size: 1rem;
        min-height: 48px;
    }

    .quiz-actions-row {
        gap: 0.8rem;
        flex-direction: column;
    }
}