body {
    font-family: Arial, sans-serif;
    background-color: #f0f0f0;
    margin: 0;
    padding: 20px;
    display: flex;
    justify-content: center;
    align-items: flex-start;
    min-height: 100vh;
}

.container {
    background-color: #e8e8e8;
    border: 1px solid #ccc;
    border-radius: 5px;
    padding: 20px;
    width: 500px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

h1 {
    text-align: center;
    margin: 0 0 15px 0;
    font-size: 24px;
    color: #333;
}

.description {
    text-align: center;
    margin: 0 0 20px 0;
    color: #666;
    font-size: 14px;
    line-height: 1.4;
}

.settings {
    margin-bottom: 20px;
}

.operation-group {
    margin-bottom: 15px;
}

.operation-group label {
    display: flex;
    align-items: center;
    font-weight: bold;
    margin-bottom: 5px;
}

.operation-group input[type="checkbox"] {
    margin-right: 8px;
}

.range-inputs {
    margin-left: 20px;
    font-size: 14px;
    color: #555;
}

.range-inputs input[type="number"] {
    width: 50px;
    padding: 2px 5px;
    border: 1px solid #ccc;
    border-radius: 3px;
}

.sub-note {
    margin-left: 20px;
    font-size: 14px;
    color: #777;
    font-style: italic;
}

.duration-group {
    margin: 20px 0;
    font-weight: bold;
}

.duration-group select {
    margin-left: 10px;
    padding: 5px;
    border: 1px solid #ccc;
    border-radius: 3px;
}

#start-btn, #restart-btn {
    background-color: #ddd;
    border: 1px solid #ccc;
    padding: 10px 20px;
    font-size: 16px;
    border-radius: 3px;
    cursor: pointer;
    display: block;
    margin: 20px auto 0;
}

#start-btn:hover, #restart-btn:hover {
    background-color: #ccc;
}

.game-area {
    text-align: center;
}

.game-header {
    display: flex;
    justify-content: space-between;
    margin-bottom: 30px;
    font-size: 18px;
    font-weight: bold;
}

.equation {
    font-size: 48px;
    font-weight: bold;
    margin: 40px 0;
    color: #333;
    min-height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.answer-section {
    margin-top: 30px;
}

#answer-input {
    font-size: 24px;
    padding: 10px 15px;
    border: 2px solid #ccc;
    border-radius: 5px;
    width: 200px;
    text-align: center;
}

#answer-input:focus {
    outline: none;
    border-color: #4CAF50;
}

#feedback {
    margin-top: 15px;
    font-size: 18px;
    font-weight: bold;
    min-height: 25px;
}

.feedback-correct {
    color: #4CAF50;
}

.feedback-incorrect {
    color: #f44336;
}

.results {
    text-align: center;
}

.results h2 {
    color: #333;
    margin-bottom: 20px;
}

.stats {
    background-color: #f9f9f9;
    border: 1px solid #ddd;
    border-radius: 5px;
    padding: 20px;
    margin-bottom: 20px;
}

.stats div {
    margin: 10px 0;
    font-size: 16px;
}

.stats span {
    font-weight: bold;
    color: #333;
}