:root {
    --primary: #1a73e8;
    --success: #34a853;
    --danger: #ea4335;
    --warning: #fbbc04;
}

.progress-bar {
    background: #e0e0e0;
    border-radius: 4px;
    height: 8px;
    position: relative;
    width: 100%;
}

.progress-bar .fill {
    border-radius: 4px;
    height: 100%;
    position: absolute;
}

.progress-bar .fill.low {
    background: var(--danger);
}

.progress-bar .fill.mid {
    background: var(--warning);
}

.progress-bar .fill.high {
    background: var(--success);
}

.range-bar {
    background: #e0e0e0;
    border-radius: 4px;
    height: 6px;
    position: relative;
    width: 100%;
}

.range-bar .range {
    background: var(--primary);
    border-radius: 4px;
    height: 100%;
    position: absolute;
    opacity: 0.6;
}

.range-bar .midpoint {
    background: var(--primary);
    border-radius: 50%;
    height: 10px;
    position: absolute;
    top: -2px;
    width: 10px;
}

.quiz-choices label {
    cursor: pointer;
    display: block;
    margin-bottom: 0.5rem;
    padding: 0.75rem 1rem;
}

.quiz-choices input[type="radio"] {
    margin-right: 0.75rem;
}

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

.incorrect {
    color: var(--danger);
}

.dont-know {
    color: var(--warning);
}

.difficulty-badge {
    display: inline-block;
    font-size: 0.75rem;
    font-weight: 600;
    padding: 0.15rem 0.5rem;
    border-radius: 999px;
    text-transform: uppercase;
    letter-spacing: 0.03em;
    vertical-align: middle;
}

.difficulty-badge.easy {
    background: #e8f5e9;
    color: #2e7d32;
}

.difficulty-badge.medium {
    background: #fff3e0;
    color: #e65100;
}

.difficulty-badge.hard {
    background: #ffebee;
    color: #c62828;
}

.card {
    border: 1px solid #ddd;
    border-radius: 8px;
    padding: 1.5rem;
    margin-bottom: 1rem;
}

.card:hover {
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.stats-grid {
    display: grid;
    gap: 1rem;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
}

.password-group {
    display: flex;
    gap: 0;
}

.password-group input {
    flex: 1;
    border-top-right-radius: 0;
    border-bottom-right-radius: 0;
}

.password-group button {
    border-top-left-radius: 0;
    border-bottom-left-radius: 0;
    margin: 0;
    white-space: nowrap;
}

.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1rem;
}

@media (max-width: 768px) {
    .stats-grid {
        grid-template-columns: 1fr;
    }

    .kbd-hint {
        display: none !important;
    }
}