:root {
    --bg-color: #0f172a;
    --card-bg: #1e293b;
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    --correct-color: #10b981;
    --incorrect-color: #ef4444;
    --border-color: #334155;
    --border-radius: 12px;
    --transition: all 0.3s ease;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
    line-height: 1.6;
}

.app-container {
    width: 100%;
    max-width: 700px;
}

header {
    margin-bottom: 30px;
    text-align: center;
}

h1 {
    font-size: 2.5rem;
    margin-bottom: 15px;
    background: linear-gradient(to right, #60a5fa, #a78bfa);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.progress-container {
    width: 100%;
    height: 8px;
    background-color: var(--card-bg);
    border-radius: 4px;
    margin-bottom: 10px;
    overflow: hidden;
}

.progress-bar {
    height: 100%;
    background-color: var(--primary-color);
    width: 0%;
    transition: width 0.4s ease;
}

#progress-text {
    color: var(--text-muted);
    font-size: 0.9rem;
    font-weight: 500;
}

#score-display {
    margin-top: 5px;
    font-weight: 600;
    color: var(--text-main);
}

.card {
    background-color: var(--card-bg);
    border-radius: var(--border-radius);
    padding: 30px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.2);
    border: 1px solid var(--border-color);
}

#question-text {
    font-size: 1.3rem;
    margin-bottom: 25px;
    font-weight: 600;
}

.options-grid {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.option-btn {
    background-color: transparent;
    border: 2px solid var(--border-color);
    color: var(--text-main);
    padding: 15px 20px;
    border-radius: var(--border-radius);
    font-size: 1rem;
    font-family: inherit;
    text-align: left;
    cursor: pointer;
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.option-btn:hover:not(:disabled) {
    border-color: var(--primary-color);
    background-color: rgba(59, 130, 246, 0.1);
}

.option-btn:disabled {
    cursor: not-allowed;
    opacity: 0.7;
}

.option-btn.correct {
    background-color: rgba(16, 185, 129, 0.15);
    border-color: var(--correct-color);
    color: var(--correct-color);
}

.option-btn.incorrect {
    background-color: rgba(239, 68, 68, 0.15);
    border-color: var(--incorrect-color);
    color: var(--incorrect-color);
}

#feedback-container {
    margin-top: 25px;
    padding-top: 20px;
    border-top: 1px solid var(--border-color);
    text-align: center;
    animation: fadeIn 0.4s ease;
}

#feedback-text {
    font-size: 1.4rem;
    margin-bottom: 10px;
}

#feedback-text.success {
    color: var(--correct-color);
}

#feedback-text.error {
    color: var(--incorrect-color);
}

#explanation-text {
    color: var(--text-muted);
    font-size: 0.95rem;
    margin-bottom: 20px;
}

.btn {
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 12px 24px;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    font-family: inherit;
}

.btn:hover {
    background-color: var(--primary-hover);
    transform: translateY(-2px);
}

.btn-large {
    padding: 15px 30px;
    font-size: 1.1rem;
}

#results-container {
    text-align: center;
}

.score-circle {
    width: 150px;
    height: 150px;
    border-radius: 50%;
    background: conic-gradient(var(--primary-color) 0%, var(--card-bg) 0%);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    margin: 30px auto;
    position: relative;
    border: 4px solid var(--border-color);
}

#final-score {
    font-size: 3rem;
    font-weight: 700;
    line-height: 1;
}

.total-text {
    font-size: 0.9rem;
    color: var(--text-muted);
}

#results-message {
    font-size: 1.2rem;
    margin-bottom: 25px;
    color: var(--text-muted);
}

.hidden {
    display: none !important;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

@media (max-width: 600px) {
    .card {
        padding: 20px;
    }
    h1 {
        font-size: 2rem;
    }
}