body {
    font-family: 'Inter', sans-serif;
    background-color: #f8fafc;
}

/* Custom Scrollbar for sidebar */
.sidebar-scroll::-webkit-scrollbar {
    width: 6px;
}

.sidebar-scroll::-webkit-scrollbar-track {
    background: transparent;
}

.sidebar-scroll::-webkit-scrollbar-thumb {
    background-color: #cbd5e1;
    border-radius: 20px;
}

/* Transitions */
.topic-header {
    transition: background-color 0.2s ease, color 0.2s ease;
}

.subtopic-item {
    transition: all 0.2s ease;
}

.subtopic-item.active {
    background-color: #eff6ff;
    color: #2563eb;
    border-right: 3px solid #2563eb;
    font-weight: 500;
}

.subtopic-item:hover:not(.active) {
    background-color: #f1f5f9;
}

/* Content Area Animations */
#content-area {
    transition: opacity 0.3s ease, transform 0.3s ease;
}

.content-loading {
    opacity: 0;
    transform: translateY(10px);
}

.content-loaded {
    opacity: 1;
    transform: translateY(0);
}

/* Loader */
.loader {
    border: 3px solid #f3f3f3;
    border-radius: 50%;
    border-top: 3px solid #2563eb;
    width: 24px;
    height: 24px;
    -webkit-animation: spin 1s linear infinite; /* Safari */
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}