:root {
    --primary-color: #4a90e2;
    --success-color: #50e3c2;
    --error-color: #e35050;
    --light-bg: #f7f9fc;
    --dark-text: #333;
    --light-text: #fff;
    --border-color: #ddd;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--light-bg);
    color: var(--dark-text);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    padding: 1rem;
    box-sizing: border-box;
}

.container {
    width: 100%;
    max-width: 500px;
    background-color: var(--light-text);
    border-radius: 12px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    padding: 2rem;
    text-align: center;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 1rem;
}

header h1 {
    margin: 0;
    font-size: 1.5rem;
    color: var(--primary-color);
}

.scoreboard {
    font-size: 1rem;
}

.settings-btn {
    background: none;
    border: none;
    font-size: 1.8rem;
    cursor: pointer;
    color: #888;
    transition: color 0.3s;
}
.settings-btn:hover {
    color: var(--primary-color);
}

.problem-container {
    font-size: 3rem;
    font-weight: bold;
    margin-bottom: 2rem;
    letter-spacing: 2px;
    min-height: 60px;
}

.answer-area {
    margin-bottom: 1.5rem;
    min-height: 120px; /* 预留空间，防止界面跳动 */
}

#answer-input {
    width: 80%;
    padding: 0.8rem;
    font-size: 2rem;
    text-align: center;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    outline: none;
    transition: border-color 0.3s;
}

#answer-input:focus {
    border-color: var(--primary-color);
}

.choice-buttons {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

.choice-btn {
    padding: 1rem;
    font-size: 1.5rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    background-color: var(--light-text);
    cursor: pointer;
    transition: background-color 0.3s, color 0.3s, transform 0.2s;
}
.choice-btn:hover:not(:disabled) {
    background-color: var(--primary-color);
    color: var(--light-text);
    transform: translateY(-3px);
}
.choice-btn:disabled {
    cursor: not-allowed;
}
.choice-btn.correct {
    background-color: var(--success-color);
    border-color: var(--success-color);
    color: var(--light-text);
}
.choice-btn.incorrect {
    background-color: var(--error-color);
    border-color: var(--error-color);
    color: var(--light-text);
}

.feedback-area {
    min-height: 30px;
    font-size: 1.2rem;
    font-weight: bold;
    margin-bottom: 1.5rem;
}

.feedback-area.correct { color: var(--success-color); }
.feedback-area.incorrect { color: var(--error-color); }

.main-btn {
    width: 100%;
    padding: 1rem;
    font-size: 1.2rem;
    font-weight: bold;
    color: var(--light-text);
    background-color: var(--primary-color);
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: background-color 0.3s, transform 0.2s;
}
.main-btn:hover {
    background-color: #357abd;
    transform: translateY(-2px);
}

/* 设置弹窗样式 */
#settings-dialog {
    border: none;
    border-radius: 12px;
    box-shadow: 0 0 30px rgba(0, 0, 0, 0.2);
    padding: 2rem;
    width: 90%;
    max-width: 450px;
}
#settings-dialog::backdrop {
    background: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(3px);
}
#settings-form h2 {
    margin-top: 0;
    color: var(--primary-color);
}
.form-group {
    margin-bottom: 1.5rem;
    text-align: left;
}
.form-group label, .form-group p {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: bold;
}
.form-group input[type="number"] {
    width: 100%;
    padding: 0.5rem;
    font-size: 1rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    box-sizing: border-box;
}
.checkbox-group, .radio-group {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
}
.checkbox-group input, .radio-group input {
    margin-right: 0.3rem;
}
.dialog-actions {
    display: flex;
    gap: 1rem;
    margin-top: 2rem;
}
.dialog-actions button {
    flex: 1;
    padding: 0.8rem;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: bold;
    cursor: pointer;
    transition: background-color 0.3s;
}
.dialog-actions button[type="button"] {
    background-color: #eee;
    border: 1px solid var(--border-color);
    color: var(--dark-text);
}
.dialog-actions button[type="button"]:hover {
    background-color: #ddd;
}

/* 响应式设计 */
@media (max-width: 480px) {
    .container {
        padding: 1rem;
    }
    header {
        flex-direction: column;
        gap: 1rem;
    }
    .problem-container {
        font-size: 2.5rem;
    }
    .choice-btn {
        font-size: 1.2rem;
    }
}