:root {
    --primary-color: #326ce5;
    --success-color: #28a745;
    --info-color: #17a2b8;
    --warning-color: #ffc107;
    --danger-color: #dc3545;
    --dark-color: #343a40;
    --light-bg: #f8f9fa;
    --sidebar-width: 260px;
}

body {
    font-family: 'Roboto', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    line-height: 1.6;
    margin: 0;
    padding: 0;
}

/* Sidebar Navigation */
.sidebar {
    width: var(--sidebar-width);
    height: 100vh;
    position: fixed;
    left: 0;
    top: 0;
    background-color: var(--primary-color);
    color: white;
    overflow-y: auto;
    z-index: 1000;
    box-shadow: 2px 0 8px rgba(0, 0, 0, 0.1);
}

.sidebar-header {
    padding: 1.5rem;
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-size: 1.25rem;
    font-weight: 500;
}

.sidebar-header .material-icons {
    font-size: 2rem;
}

.sidebar-nav {
    list-style: none;
    padding: 0;
    margin: 0;
}

.sidebar-nav .nav-item {
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.sidebar-nav .nav-link {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 1rem 1.5rem;
    color: rgba(255, 255, 255, 0.85);
    text-decoration: none;
    transition: all 0.3s ease;
}

.sidebar-nav .nav-link:hover {
    background-color: rgba(255, 255, 255, 0.1);
    color: white;
}

.sidebar-nav .nav-link.active {
    background-color: rgba(255, 255, 255, 0.15);
    color: white;
    border-left: 4px solid white;
    padding-left: calc(1.5rem - 4px);
}

.sidebar-nav .nav-link .material-icons {
    font-size: 1.5rem;
}

/* Main Content */
.main-content {
    margin-left: var(--sidebar-width);
    flex: 1;
    min-height: 100vh;
}

/* Hero Section */
.hero-section {
    background: linear-gradient(135deg, var(--primary-color) 0%, #1a237e 100%);
    color: white;
    padding: 80px 0;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.hero-section h1 {
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
}

/* Material Design Button */
.btn-raised {
    box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.14),
                0 3px 1px -2px rgba(0, 0, 0, 0.12),
                0 1px 5px 0 rgba(0, 0, 0, 0.2);
    transition: all 0.3s ease;
    font-weight: 500;
    letter-spacing: 0.5px;
}

.btn-raised:hover {
    box-shadow: 0 4px 5px 0 rgba(0, 0, 0, 0.14),
                0 1px 10px 0 rgba(0, 0, 0, 0.12),
                0 2px 4px -1px rgba(0, 0, 0, 0.2);
    transform: translateY(-2px);
}

/* Concept Cards */
.concept-card {
    border: none;
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
    transition: all 0.3s ease;
    overflow: hidden;
}

.concept-card:hover {
    transform: translateY(-8px);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.15);
}

.concept-card .card-body {
    padding: 2rem;
}

.material-icons-large {
    font-size: 64px !important;
}

.concept-btn {
    margin-top: 1rem;
    border-radius: 24px;
    padding: 0.5rem 1.5rem;
    font-weight: 500;
}

/* Accordion Styles */
.accordion-button {
    font-weight: 500;
    background-color: var(--light-bg);
}

.accordion-button:not(.collapsed) {
    background-color: var(--primary-color);
    color: white;
}

.accordion-body pre {
    background-color: #2d2d2d;
    color: #f8f8f2;
    padding: 1.5rem;
    border-radius: 8px;
    overflow-x: auto;
    font-size: 0.9rem;
    margin: 1rem 0;
}

.accordion-body code {
    font-family: 'Monaco', 'Menlo', 'Ubuntu Mono', monospace;
}

/* Resource Cards */
.resource-card {
    border: none;
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
    transition: all 0.3s ease;
    height: 100%;
}

.resource-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 6px 20px rgba(0, 0, 0, 0.12);
}

.resource-card .card-body {
    padding: 1.5rem;
}

.resource-link {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.3s ease;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.resource-link:hover {
    color: #1a237e;
    text-decoration: underline;
}

/* Concept Detail Content */
.concept-detail-content {
    padding: 1.5rem;
    border-top: 1px solid #dee2e6;
    background-color: #f8f9fa;
    animation: slideDown 0.3s ease-out;
}

.concept-detail-content h5 {
    color: var(--primary-color);
    margin-top: 1rem;
    margin-bottom: 0.75rem;
    font-weight: 600;
}

.concept-detail-content h5:first-child {
    margin-top: 0;
}

.concept-detail-content p {
    margin-bottom: 1rem;
    line-height: 1.7;
}

.concept-detail-content ul {
    padding-left: 1.5rem;
    margin-bottom: 1rem;
}

.concept-detail-content li {
    margin-bottom: 0.5rem;
    line-height: 1.6;
}

.concept-detail-content pre {
    background-color: #2d2d2d;
    color: #f8f8f2;
    padding: 1rem;
    border-radius: 8px;
    overflow-x: auto;
    font-size: 0.85rem;
    margin: 1rem 0;
}

.concept-detail-content code {
    font-family: 'Monaco', 'Menlo', 'Ubuntu Mono', monospace;
}

.concept-detail-content strong {
    color: #495057;
}

@keyframes slideDown {
    from {
        opacity: 0;
        max-height: 0;
        overflow: hidden;
    }
    to {
        opacity: 1;
        max-height: 2000px;
    }
}

/* Responsive Design */
@media (max-width: 992px) {
    .sidebar {
        width: 100%;
        height: auto;
        position: relative;
    }
    
    .main-content {
        margin-left: 0;
    }
    
    .sidebar-nav {
        display: flex;
        overflow-x: auto;
        padding: 0.5rem;
    }
    
    .sidebar-nav .nav-item {
        border-bottom: none;
        border-right: 1px solid rgba(255, 255, 255, 0.1);
        flex-shrink: 0;
    }
    
    .sidebar-nav .nav-link {
        white-space: nowrap;
        padding: 0.75rem 1rem;
    }
    
    .sidebar-nav .nav-link.active {
        border-left: none;
        border-bottom: 4px solid white;
        padding-left: 1rem;
    }
}

@media (max-width: 768px) {
    .hero-section {
        padding: 60px 0;
    }
    
    .hero-section h1 {
        font-size: 2.5rem;
    }
    
    .concept-card .card-body {
        padding: 1.5rem;
    }
    
    .material-icons-large {
        font-size: 48px !important;
    }
}

/* Smooth Scrolling */
html {
    scroll-behavior: smooth;
}

/* Section Spacing */
section {
    position: relative;
    padding: 4rem 0;
}

section#home {
    padding: 0;
}

/* Animations */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.concept-card {
    animation: fadeInUp 0.6s ease-out;
}

.concept-card:nth-child(1) { animation-delay: 0.1s; }
.concept-card:nth-child(2) { animation-delay: 0.2s; }
.concept-card:nth-child(3) { animation-delay: 0.3s; }
.concept-card:nth-child(4) { animation-delay: 0.4s; }
.concept-card:nth-child(5) { animation-delay: 0.5s; }
.concept-card:nth-child(6) { animation-delay: 0.6s; }