* {
    box-sizing: border-box;
    font-family: Arial, sans-serif;
}

body {
    margin: 0;
    background: #0f172a;
    color: #e5e7eb;
}

.app {
    max-width: 1000px;
    margin: auto;
    padding: 20px;
}

h1 {
    text-align: center;
    margin-bottom: 25px;
}

.chapters {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
    gap: 12px;
    margin-bottom: 30px;
}

.chapter {
    background: #1e293b;
    padding: 12px;
    border-radius: 8px;
    cursor: pointer;
    text-align: center;
    font-size: 14px;
}

.chapter:hover {
    background: #334155;
}

.quiz {
    background: #020617;
    padding: 20px;
    border-radius: 10px;
}

.question {
    margin-bottom: 25px;
}

.options button {
    width: 100%;
    margin-top: 8px;
    padding: 10px;
    background: #1e293b;
    border: none;
    border-radius: 6px;
    color: #e5e7eb;
    cursor: pointer;
}

.options button:hover {
    background: #334155;
}

.not-available {
    text-align: center;
    font-size: 18px;
    opacity: 0.7;
}