* {
    font-family: 'Inter', sans-serif;
    box-sizing: border-box;
}

.sidebar {
    position: fixed;
    left: 0;
    top: 0;
    bottom: 0;
    width: 14rem;
    background: #111827;
    border-right: 1px solid #374151;
    display: flex;
    flex-direction: column;
    z-index: 40;
    overflow-y: auto;
}

.nav-btn {
    display: block;
    width: 100%;
    text-align: left;
    padding: 0.6rem 1rem;
    border-radius: 0.5rem;
    color: #9ca3af;
    font-size: 0.9rem;
    transition: all 0.15s;
    border: none;
    background: none;
    cursor: pointer;
}

.nav-btn:hover {
    background: #1f2937;
    color: #e5e7eb;
}

.nav-btn.active {
    background: #1e3a5f;
    color: #60a5fa;
    font-weight: 600;
}

.card {
    background: #1f2937;
    border: 1px solid #374151;
    border-radius: 0.75rem;
    padding: 1.25rem;
}

.flashcard {
    animation: fadeIn 0.3s ease;
}

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

.option-btn {
    border: 1px solid #4b5563;
    font-size: 0.95rem;
    cursor: pointer;
}

.option-btn:disabled {
    cursor: default;
}

/* Mobile */
@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-100%);
        transition: transform 0.3s ease;
    }
    .sidebar.open {
        transform: translateX(0);
    }
    main {
        margin-left: 0 !important;
    }
}

/* Scrollbar */
::-webkit-scrollbar {
    width: 6px;
}
::-webkit-scrollbar-track {
    background: #111827;
}
::-webkit-scrollbar-thumb {
    background: #374151;
    border-radius: 3px;
}

details summary {
    list-style: none;
}
details summary::-webkit-details-marker {
    display: none;
}
details[open] {
    border-color: #4b5563;
}