:root {
    --primary-color: #007bff;
    --secondary-color: #28a745;
    --danger-color: #dc3545;
    --warning-color: #ffc107;
    --light-bg: #f8f9fa;
    --white: #ffffff;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --border-radius: 12px;
    --transition: all 0.2s ease; /* Giảm time từ 0.3s xuống 0.2s */
    --light-red: #f8d7da;
    --light-green: #d4edda;
}

body { 
    font-family: 'Roboto', sans-serif; 
    max-width: 900px; 
    margin: 0 auto; 
    padding: 20px; 
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: #333;
    line-height: 1.6;
}

h1, h2 { 
    color: var(--white); 
    text-align: center; 
    text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
}

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

.warning { 
    background: rgba(255, 193, 7, 0.9); 
    color: #333; 
    padding: 15px; 
    border-radius: var(--border-radius); 
    text-align: center; 
    font-weight: 500; 
    box-shadow: var(--shadow);
}

.progress { 
    text-align: center; 
    margin: 20px 0; 
    font-weight: 500; 
    background: rgba(255,255,255,0.2); 
    padding: 15px; 
    border-radius: var(--border-radius); 
    color: var(--white);
}

.progress-bar {
    width: 100%;
    height: 8px;
    background: rgba(255,255,255,0.3);
    border-radius: 4px;
    overflow: hidden;
    margin-top: 10px;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--secondary-color), var(--primary-color));
    width: 0%;
    transition: width 0.5s ease;
}

.section { 
    margin-bottom: 40px; 
    background: var(--white); 
    padding: 30px; 
    border-radius: var(--border-radius); 
    box-shadow: var(--shadow);
    transition: var(--transition);
}

.section:hover { 
    transform: translateY(-2px); 
    box-shadow: 0 8px 15px rgba(0,0,0,0.15);
}

.question { 
    margin-bottom: 25px; 
    padding: 20px; 
    border: 1px solid #e9ecef; 
    border-radius: var(--border-radius); 
    background: #fafafa;
    transition: var(--transition);
}

.question:hover {
    border-color: var(--primary-color);
    background: #f0f8ff;
}

.question h3 { 
    margin-top: 0; 
    color: var(--primary-color); 
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 10px;
}

.question h3 i { color: var(--secondary-color); }

.options { 
    list-style: none; 
    padding: 0; 
}

.options li { 
    margin-bottom: 12px; 
    padding: 12px; 
    background: var(--white); 
    border-radius: 8px; 
    border-left: 4px solid var(--primary-color);
    will-change: transform; /* Optimize rendering cho hover */
    transition: var(--transition);
    cursor: pointer;
}

.options li:hover { 
    background: #e3f2fd; 
    transform: translateX(3px); /* Giảm từ 5px để mượt hơn */
}

.options input[type="radio"] { 
    margin-right: 12px; 
    transform: scale(1.3); 
    accent-color: var(--primary-color);
    pointer-events: none; /* Tránh conflict với label */
}

.options label {
    cursor: pointer;
    display: flex;
    align-items: center;
    width: 100%;
    pointer-events: all; /* Đảm bảo label clickable mượt */
    user-select: none; /* Tránh select text khi click */
}

.true-false { 
    display: grid; 
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); 
    gap: 15px; 
    margin-top: 15px; 
}

.true-false .option-group { 
    display: flex; 
    flex-direction: column; 
    gap: 8px; 
    background: var(--white); 
    padding: 15px; 
    border-radius: 8px; 
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    will-change: background-color;
}

.true-false label { 
    display: flex; 
    align-items: center; 
    background: linear-gradient(135deg, #e8f5e8, #d4edda); 
    padding: 10px; 
    border-radius: 6px; 
    cursor: pointer; 
    transition: var(--transition);
    font-weight: 400;
    user-select: none;
}

.true-false label:hover {
    background: linear-gradient(135deg, #c8e6c9, #a5d6a7);
}

.true-false input[type="radio"] { 
    margin-right: 8px; 
    transform: scale(1.2); 
    accent-color: var(--secondary-color);
    pointer-events: none;
}

input[type="text"] { 
    width: 100%; 
    padding: 12px; 
    border: 2px solid #dee2e6; 
    border-radius: 8px; 
    font-size: 16px; 
    transition: var(--transition);
    font-family: 'Roboto', sans-serif;
}

input[type="text"]:focus {
    border-color: var(--primary-color);
    outline: none;
    box-shadow: 0 0 0 0.2rem rgba(0,123,255,.25);
}

button { 
    background: linear-gradient(135deg, var(--secondary-color), #20c997); 
    color: var(--white); 
    padding: 15px 40px; 
    border: none; 
    border-radius: var(--border-radius); 
    cursor: pointer; 
    font-size: 18px; 
    font-weight: 500;
    display: block; 
    margin: 30px auto; 
    transition: var(--transition);
    box-shadow: var(--shadow);
}

button:hover { 
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(40,167,69,0.3);
}

button:active {
    transform: translateY(0);
}

#result { 
    display: none; 
    margin-top: 30px; 
    padding: 30px; 
    background: linear-gradient(135deg, #d4edda, #c3e6cb); 
    border: 1px solid #c3e6cb; 
    border-radius: var(--border-radius); 
    box-shadow: var(--shadow);
}

.correct { 
    color: var(--secondary-color); 
    font-weight: bold; 
    background: rgba(40,167,69,0.2); 
    padding: 4px 8px; 
    border-radius: 6px; 
}

.incorrect { 
    color: var(--danger-color); 
    font-weight: bold; 
    background: rgba(220,53,69,0.2); 
    padding: 4px 8px; 
    border-radius: 6px; 
}

.score { 
    text-align: center; 
    font-size: 24px; 
    margin: 20px 0; 
    font-weight: 700;
    color: var(--secondary-color);
}

.score-banner {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: linear-gradient(135deg, var(--secondary-color), #20c997);
    color: white;
    padding: 15px;
    text-align: center;
    z-index: 1000;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.score-banner h2 {
    margin: 0;
    color: white;
}

.result-question {
    margin-bottom: 20px;
    padding: 15px;
    border: 1px solid #ddd;
    border-radius: 8px;
    background: white;
}

.result-options {
    list-style: none;
    padding: 0;
}

.result-options li {
    padding: 8px;
    margin: 5px 0;
    border-radius: 5px;
    border-left: 3px solid transparent;
}

.result-options .wrong-selected {
    background-color: var(--light-red);
    border-left-color: var(--danger-color);
}

.result-options .correct-answer {
    background-color: var(--light-green);
    border-left-color: var(--secondary-color);
}

.result-options .correct-selected {
    background-color: var(--light-green);
    border-left-color: var(--secondary-color);
}

/* Responsive */
@media (max-width: 768px) {
    body { padding: 10px; }
    h1 { font-size: 2em; }
    .true-false { grid-template-columns: 1fr; }
    .section { padding: 20px; }
}
.section h2 {
  color: #12243d;}