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

:root {
    --primary-color: #2563eb;
    --primary-dark: #1d4ed8;
    --secondary-color: #3b82f6;
    --success-color: #0ea5e9;
    --warning-color: #0284c7;
    --danger-color: #ef4444;
    --text-dark: #1e293b;
    --text-light: #64748b;
    --bg-light: #f1f5f9;
    --bg-white: #ffffff;
    --border-color: #cbd5e1;
    --shadow: 0 1px 3px rgba(37, 99, 235, 0.1);
    --shadow-lg: 0 10px 25px rgba(37, 99, 235, 0.15);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: var(--text-dark);
    background: linear-gradient(135deg, #1e40af 0%, #0ea5e9 100%);
    min-height: 100vh;
    padding: 20px;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    background: var(--bg-white);
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    overflow: hidden;
}

/* Header */
header {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    padding: 40px 30px;
    text-align: center;
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
    font-weight: 700;
}

.subtitle {
    font-size: 1.1rem;
    opacity: 0.95;
}

/* Tabs Navigation */
.tabs {
    display: flex;
    gap: 0;
    background: var(--bg-light);
    padding: 0;
    border-bottom: 2px solid var(--border-color);
    overflow-x: auto;
    flex-wrap: wrap;
}

.tab-btn {
    flex: 1;
    min-width: 120px;
    padding: 16px 20px;
    background: transparent;
    border: none;
    color: var(--text-light);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    border-bottom: 3px solid transparent;
}

.tab-btn:hover {
    background: rgba(37, 99, 235, 0.1);
    color: var(--primary-color);
}

.tab-btn.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
    background: var(--bg-white);
}

.tab-btn.quiz-tab {
    background: linear-gradient(135deg, var(--success-color), #0284c7);
    color: white;
    margin-left: auto;
}

.tab-btn.quiz-tab:hover {
    background: linear-gradient(135deg, #0284c7, #0369a1);
}

.tab-btn.quiz-tab.active {
    background: var(--success-color);
    color: white;
}

/* Main Content */
.content {
    padding: 40px 30px;
    min-height: 500px;
}

.tab-content {
    display: none;
    animation: fadeIn 0.3s ease;
}

.tab-content.active {
    display: block;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.tab-content h2 {
    font-size: 2rem;
    color: var(--primary-color);
    margin-bottom: 25px;
    padding-bottom: 15px;
    border-bottom: 3px solid var(--primary-color);
}

.approach-card {
    background: var(--bg-light);
    padding: 30px;
    border-radius: 12px;
    border-left: 4px solid var(--primary-color);
}

.approach-card h3 {
    font-size: 1.5rem;
    color: var(--text-dark);
    margin-top: 25px;
    margin-bottom: 15px;
}

.approach-card h3:first-child {
    margin-top: 0;
}

.approach-card h4 {
    font-size: 1.2rem;
    color: var(--text-dark);
    margin-bottom: 10px;
}

.approach-card p {
    color: var(--text-light);
    margin-bottom: 15px;
    font-size: 1.05rem;
}

.approach-card ul {
    list-style: none;
    padding-left: 0;
}

.approach-card ul li {
    padding: 10px 0 10px 30px;
    position: relative;
    color: var(--text-light);
}

.approach-card ul li::before {
    content: "→";
    position: absolute;
    left: 0;
    color: var(--primary-color);
    font-weight: bold;
    font-size: 1.2rem;
}

.two-column {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 30px;
    margin-top: 20px;
}

.example-box {
    background: white;
    padding: 20px;
    border-radius: 8px;
    border-left: 4px solid var(--secondary-color);
    margin: 20px 0;
}

.example-box strong {
    color: var(--primary-color);
}

/* Quiz Styles */
.quiz-container {
    max-width: 800px;
    margin: 0 auto;
}

.quiz-start {
    text-align: center;
    padding: 60px 30px;
}

.quiz-start p {
    font-size: 1.2rem;
    color: var(--text-light);
    margin-bottom: 30px;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    border: none;
    padding: 14px 32px;
    font-size: 1.1rem;
    font-weight: 600;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-primary:active {
    transform: translateY(0);
}

.quiz-progress {
    margin-bottom: 30px;
}

#question-number {
    display: block;
    color: var(--text-light);
    margin-bottom: 10px;
    font-weight: 600;
}

.progress-bar {
    width: 100%;
    height: 8px;
    background: var(--bg-light);
    border-radius: 4px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    transition: width 0.3s ease;
    width: 0%;
}

#question-container {
    background: var(--bg-light);
    padding: 30px;
    border-radius: 12px;
    margin-bottom: 25px;
}

.question-text {
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--text-dark);
    margin-bottom: 25px;
}

.answer-options {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.answer-btn {
    background: white;
    border: 2px solid var(--border-color);
    padding: 16px 20px;
    text-align: left;
    font-size: 1.05rem;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s ease;
    color: var(--text-dark);
}

.answer-btn:hover {
    border-color: var(--primary-color);
    background: rgba(37, 99, 235, 0.05);
    transform: translateX(5px);
}

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

.answer-btn.correct {
    background: var(--success-color);
    color: white;
    border-color: var(--success-color);
}

.answer-btn.incorrect {
    background: var(--danger-color);
    color: white;
    border-color: var(--danger-color);
}

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

.quiz-navigation {
    text-align: center;
}

/* Quiz Results */
.quiz-results {
    text-align: center;
    padding: 40px 20px;
}

.quiz-results h3 {
    font-size: 2rem;
    color: var(--primary-color);
    margin-bottom: 30px;
}

.score-display {
    margin: 40px 0;
}

.score-circle {
    width: 200px;
    height: 200px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 20px;
    box-shadow: var(--shadow-lg);
}

#score-percentage {
    font-size: 3.5rem;
    font-weight: 700;
    color: white;
}

#score-text {
    font-size: 1.3rem;
    color: var(--text-dark);
    margin-bottom: 20px;
}

#score-message {
    background: var(--bg-light);
    padding: 20px;
    border-radius: 8px;
    margin: 30px 0;
    font-size: 1.1rem;
    color: var(--text-light);
}

/* Footer */
footer {
    background: var(--bg-light);
    padding: 20px;
    text-align: center;
    color: var(--text-light);
    border-top: 1px solid var(--border-color);
}

/* Responsive Design */
@media (max-width: 768px) {
    body {
        padding: 10px;
    }

    header h1 {
        font-size: 1.8rem;
    }

    .subtitle {
        font-size: 1rem;
    }

    .content {
        padding: 20px 15px;
    }

    .tab-content h2 {
        font-size: 1.5rem;
    }

    .approach-card {
        padding: 20px;
    }

    .two-column {
        grid-template-columns: 1fr;
        gap: 20px;
    }

    .tab-btn {
        font-size: 0.9rem;
        padding: 12px 15px;
        min-width: 100px;
    }

    .score-circle {
        width: 150px;
        height: 150px;
    }

    #score-percentage {
        font-size: 2.5rem;
    }
}