body {
    font-family: 'Poppins', sans-serif;
    margin: 0;
    padding: 20px;
    background-color: #f0f2f5;
    display: flex;
    justify-content: center;
    align-items: flex-start;
    min-height: 100vh;
    box-sizing: border-box;
}

.quiz-container {
    background-color: #ffffff;
    padding: 25px;
    border-radius: 12px;
    box-shadow: 0 6px 15px rgba(0, 0, 0, 0.1);
    width: 100%;
    max-width: 500px;
    text-align: center;
    margin-top: 30px;
}

h1 {
    color: #2c3e50;
    margin-bottom: 25px;
    font-size: 2em;
    font-weight: 600;
}

h2 {
    color: #34495e;
    margin-bottom: 20px;
    font-size: 1.4em;
    font-weight: 500;
}

#question-counter {
    font-size: 0.95em;
    color: #7f8c8d;
    margin-bottom: 15px;
    font-weight: 400;
}

.progress-bar {
    width: 100%;
    height: 10px;
    background-color: #ecf0f1;
    border-radius: 5px;
    margin-bottom: 25px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    width: 0%;
    background-color: #27ae60;
    border-radius: 5px;
    transition: width 0.4s ease-in-out;
}

#options-container {
    display: flex;
    flex-direction: column;
    gap: 12px;
    margin-top: 25px;
}

.option-button {
    background-color: #f8f9fa;
    border: 1px solid #dee2e6;
    padding: 14px 18px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 1.05em;
    color: #34495e;
    transition: background-color 0.25s, transform 0.1s, box-shadow 0.25s;
    text-align: left;
    width: 100%;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
}

.option-button:hover:not(:disabled) {
    background-color: #e9ecef;
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

.option-button:disabled {
    cursor: not-allowed;
    opacity: 0.6;
}

.option-button.correct {
    background-color: #d4edda; /* Light green */
    border-color: #28a745;
    color: #155724;
    font-weight: 600;
    box-shadow: 0 2px 4px rgba(40, 167, 69, 0.2);
}

.option-button.incorrect {
    background-color: #f8d7da; /* Light red */
    border-color: #dc3545;
    color: #721c24;
    font-weight: 600;
    box-shadow: 0 2px 4px rgba(220, 53, 69, 0.2);
}

.nav-button {
    background-color: #3498db; /* A distinct blue */
    color: white;
    border: none;
    padding: 12px 25px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 1.1em;
    margin-top: 30px;
    width: 100%;
    box-sizing: border-box;
    transition: background-color 0.25s, transform 0.1s, box-shadow 0.25s;
    font-weight: 600;
    box-shadow: 0 4px 8px rgba(52, 152, 219, 0.3);
}

.nav-button:hover:not(:disabled) {
    background-color: #2980b9;
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(52, 152, 219, 0.4);
}

.nav-button:disabled {
    background-color: #a0c4ff;
    cursor: not-allowed;
    opacity: 0.7;
    box-shadow: none;
}

.hidden {
    display: none;
}

/* Responsive adjustments */
@media (min-width: 600px) {
    .quiz-container {
        padding: 35px;
    }

    h1 {
        font-size: 2.4em;
    }

    h2 {
        font-size: 1.6em;
    }

    .option-button, .nav-button {
        font-size: 1.15em;
    }
}