body {
    font-family: Arial, sans-serif;
    max-width: 800px;
    margin: 0 auto;
    padding: 10px 20px;
    background-color: #f5f5f5;
}

.header {
    text-align: center;
    padding: 10px;
    background-color: #4CAF50;
    color: white;
    border-radius: 10px;
    margin-bottom: 15px;
}

.header h1 {
    margin: 0 0 5px 0;
    font-size: 1.8em;
}

.header p {
    margin: 0;
    font-size: 1em;
}

.quiz-container {
    background-color: white;
    padding: 15px;
    border-radius: 10px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

.problem {
    font-size: 2em;
    text-align: center;
    margin: 15px 0;
    padding: 10px;
    background-color: #f8f9fa;
    border-radius: 8px;
}

.answer-display {
    font-size: 1.5em;
    text-align: center;
    min-height: 40px;
    margin: 15px 0;
    padding: 10px;
    background-color: #fff;
    border: 2px solid #ddd;
    border-radius: 8px;
    transition: background-color 0.3s;
}

.answer-correct {
    background-color: #C8E6C9;
    border-color: #4CAF50;
}

.answer-incorrect {
    background-color: #FFCDD2;
    border-color: #F44336;
}

.keypad {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
    max-width: 300px;
    margin: 0 auto;
}

.key {
    padding: 15px;
    font-size: 1.2em;
    border: none;
    border-radius: 8px;
    background-color: #2196F3;
    color: white;
    cursor: pointer;
    transition: background-color 0.2s;
}

.key:hover {
    background-color: #1976D2;
}

.key.back {
    background-color: #FFA726;
}

.key.back:hover {
    background-color: #FB8C00;
}

.submit-btn, .next-btn {
    display: block;
    width: 100%;
    max-width: 300px;
    margin: 15px auto;
    padding: 15px;
    font-size: 1.2em;
    border: none;
    border-radius: 8px;
    color: white;
    cursor: pointer;
    transition: background-color 0.2s;
}

.submit-btn {
    background-color: #4CAF50;
}

.submit-btn:hover {
    background-color: #388E3C;
}

.next-btn {
    background-color: #FF9800;
    display: none;
}

.next-btn:hover {
    background-color: #F57C00;
}

.back-to-menu {
    display: block;
    text-align: center;
    margin-top: 15px;
    color: #2196F3;
    text-decoration: none;
}

/* Main menu page styles */
.quiz-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 15px;
    padding: 15px;
}

.quiz-button {
    padding: 20px;
    font-size: 1.1em;
    border: none;
    border-radius: 8px;
    background-color: #2196F3;
    color: white;
    cursor: pointer;
    transition: transform 0.2s, background-color 0.2s;
}

.quiz-button:hover {
    transform: translateY(-3px);
    background-color: #1976D2;
}

.quiz-button:active {
    transform: translateY(1px);
}