body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #121212;
    color: #e0e0e0;
    line-height: 1.6;
    padding: 20px;
    margin: 0;
}

.quiz-container {
    max-width: 800px;
    margin: 0px auto;
    background: #1e1e1e;
    padding: 30px;
    border-radius: 12px;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.3);
    position: relative;
    border: 1px solid #2d2d2d;
}

h1 {
    color: #3498db;
    font-size: 1.5em;
    margin-top: 0;
    border-bottom: 2px solid #2d2d2d;
    padding-bottom: 15px;
    max-width: 65%;
}

.score-board {
    position: absolute;
    top: 25px;
    right: 30px;
    background-color: #252526;
    border: 1px solid #3e3e3e;
    padding: 10px 15px;
    border-radius: 8px;
    text-align: right;
    font-family: monospace;
    font-size: 1.05em;
}

.score-board .metrics {
    color: #00e676;
    font-weight: bold;
}

.question-box {
    margin: 30px 0;
}

.question-text {
    font-size: 1.25em;
    color: #ffffff;
    margin-bottom: 25px;
    font-weight: 500;
}

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

.option-item {
    margin-bottom: 12px;
}

.option-label {
    display: block;
    padding: 14px;
    background-color: #2a2a2a;
    border: 1px solid #3a3a3a;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s;
}

.option-label:hover {
    background-color: #333333;
    border-color: #555555;
}

input[type="radio"] {
    margin-right: 12px;
    transform: scale(1.2);
    vertical-align: middle;
}

.option-label.correct-choice {
    background-color: #1b5e20 !important;
    border-color: #00e676 !important;
    color: #ffffff;
}

.option-label.incorrect-choice {
    background-color: #b71c1c !important;
    border-color: #ff5252 !important;
    color: #ffffff;
}

.option-label.disabled {
    pointer-events: none;
    opacity: 0.6;
}

.option-label.correct-choice.disabled,
.option-label.incorrect-choice.disabled {
    opacity: 1;
}

.feedback-area {
    margin-top: 20px;
    padding: 15px;
    border-radius: 8px;
    background-color: #252526;
    border-left: 4px solid #3498db;
    display: none;
}

.feedback-title {
    font-weight: bold;
    margin-bottom: 5px;
}

.feedback-title.true {
    color: #00e676;
}

.feedback-title.false {
    color: #ff5252;
}

.action-area {
    margin-top: 25px;
    text-align: right;
}

button {
    padding: 12px 24px;
    background-color: #3498db;
    color: white;
    border: none;
    border-radius: 6px;
    font-size: 1em;
    font-weight: bold;
    cursor: pointer;
}

button:hover {
    background-color: #2980b9;
}

.summary-screen {
    text-align: center;
    padding: 20px 0;
}

.summary-screen h2 {
    color: #00e676;
}

/* CSS tạo dấu mũ Góc trên đầu chữ cái giống SGK Toán Việt Nam */
.math-angle {
    position: relative;
    display: inline-block;
    padding-top: 4px;
    margin: 0 2px;
    font-style: normal;
}

.math-angle::before {
    content: "^";
    position: absolute;
    top: -6px;
    left: 50%;
    transform: translateX(-50%) scaleX(1.8);
    font-size: 0.7em;
    font-weight: bold;
}