body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Arial, sans-serif;
    background-color: #f0f2f5;
    color: #333;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
}

.container {
    background-color: #ffffff;
    padding: 2.5rem 3rem;
    border-radius: 10px;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
    text-align: center;
    max-width: 600px;
    width: 90%;
}

h1 {
    color: #2c3e50;
    margin-bottom: 0.2rem;
}

.subtitle {
    color: #6c757d;
    margin-top: 0;
    margin-bottom: 2rem;
    font-size: 0.95rem;
}

.problem-container {
    margin-bottom: 1.5rem;
}

.sentence-box {
    font-size: 1.3rem;
    margin: 1.5rem 0;
    padding: 1.5rem;
    background-color: #f8f9fa;
    border: 1px solid #dee2e6;
    border-radius: 8px;
    line-height: 1.5;
}

.highlight {
    font-weight: bold;
    color: #0056b3;
    background-color: #e9ecef;
    padding: 2px 6px;
    border-radius: 4px;
}

.input-group {
    margin: 1.5rem 0;
}

input[type="text"] {
    width: 80%;
    padding: 12px;
    font-size: 1.1rem;
    border: 2px solid #ccc;
    border-radius: 6px;
    text-align: center;
    transition: border-color 0.3s;
}

input[type="text"]:focus {
    border-color: #0056b3;
    outline: none;
}

.controls {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-top: 1rem;
}

button {
    padding: 12px 24px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    border: none;
    border-radius: 6px;
    transition: background-color 0.2s;
}

.btn-primary { background-color: #0056b3; color: white; }
.btn-primary:hover { background-color: #004494; }

.btn-secondary { background-color: #6c757d; color: white; }
.btn-secondary:hover { background-color: #5a6268; }

.hidden { display: none !important; }

.feedback-box {
    margin-top: 1.5rem;
    padding: 1rem 1.5rem;
    border-radius: 6px;
    text-align: left;
    font-size: 0.95rem;
}

.feedback-success {
    background-color: #d4edda;
    border: 1px solid #c3e6cb;
    color: #155724;
}

.feedback-error {
    background-color: #f8d7da;
    border: 1px solid #f5c6cb;
    color: #721c24;
}

.feedback-title {
    font-weight: bold;
    font-size: 1.1rem;
    margin-top: 0;
}

.score-container {
    margin-top: 2rem;
    font-size: 1.1rem;
    font-weight: bold;
    color: #495057;
    border-top: 1px solid #eee;
    padding-top: 1rem;
}