body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f4f4f4;
}

.container {
    display: flex;
    width: 90%;
    max-width: 1200px;
    background: white;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

.sidebar {
    width: 250px;
    background: #9c9494;
    color: white;
    padding: 15px;
}

.sidebar h3, .sidebar h4 {
    margin-bottom: 10px;
}

.sidebar label {
    display: block;
    margin-bottom: 5px;
    cursor: pointer;
}

.sidebar input {
    margin-right: 5px;
}

.content {
    flex-grow: 1;
    padding: 20px;
    text-align: center;
}

iframe {
    width: 100%;
    height: 400px;
    border: none;
    background: #fff;
}

#nextProblem {
    margin-top: 10px;
    padding: 10px 20px;
    font-size: 16px;
    background: #28a745;
    color: white;
    border: none;
    cursor: pointer;
}

#nextProblem:hover {
    background: #218838;
}

@media (max-width: 768px) {
    .container {
        flex-direction: column;
    }
    .sidebar {
        width: 100%;
        text-align: center;
    }
    iframe {
        height: 300px;
    }
}