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

:root {
    /* Color Palette */
    --bg-primary: #0a0a0f;
    --bg-secondary: #151520;
    --bg-tertiary: #1a1a2e;
    --text-primary: #e4e4e7;
    --text-secondary: #a1a1aa;
    --text-muted: #71717a;
    
    /* Accent Colors */
    --accent-cyan: #06b6d4;
    --accent-purple: #8b5cf6;
    --accent-green: #10b981;
    --accent-orange: #f97316;
    --accent-pink: #ec4899;
    --accent-yellow: #eab308;
    --accent-red: #ef4444;
    
    /* Topic-specific Colors */
    --accent-linear: var(--accent-cyan);
    --accent-tree: var(--accent-green);
    --accent-sorting: var(--accent-orange);
    --accent-graph: var(--accent-purple);
    --accent-search: var(--accent-yellow);
    
    /* Gradients */
    --gradient-primary: linear-gradient(135deg, var(--accent-cyan), var(--accent-purple));
    --gradient-secondary: linear-gradient(135deg, var(--accent-green), var(--accent-cyan));
    --gradient-tertiary: linear-gradient(135deg, var(--accent-orange), var(--accent-pink));
    --gradient-linear: linear-gradient(135deg, var(--accent-cyan), var(--accent-purple));
    --gradient-tree: linear-gradient(135deg, var(--accent-green), var(--accent-cyan));
    --gradient-sorting: linear-gradient(135deg, var(--accent-orange), var(--accent-pink));
    --gradient-graph: linear-gradient(135deg, var(--accent-purple), var(--accent-pink));

    /* Shadows and Glows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-glow: 0 0 20px rgba(6, 182, 212, 0.3);
    --glow-linear: 0 0 20px rgba(6, 182, 212, 0.3);
    --glow-tree: 0 0 20px rgba(16, 185, 129, 0.3);
    --glow-sorting: 0 0 20px rgba(249, 115, 22, 0.3);
    --glow-graph: 0 0 20px rgba(139, 92, 246, 0.3);
    
    /* Typography */
    --font-sans: 'Poppins', sans-serif;
    --font-mono: 'JetBrains Mono', monospace;
    --font-primary: var(--font-sans);
    
    /* Stripping Color */
    --bg-gradient-stripe-color: rgba(255, 255, 255, 0.03);
}

[data-theme="light"] {
    /* Color Palette */
    --bg-primary: #f2f4f8;
    --bg-secondary: #e1e6ec;
    --bg-tertiary: #cfd8df;
    --text-primary: #1c1e21;
    --text-secondary: #3f4b56;
    --text-muted: #6c7a88;

    /* Accent Colors */
    --accent-cyan: #00838f;
    --accent-purple: #5e60ce;
    --accent-green: #2e7d32;
    --accent-orange: #e76f51;
    --accent-pink: #d6336c;
    --accent-yellow: #f6c90e;
    --accent-red: #d32f2f;

    /* Gradients */
    --gradient-primary: linear-gradient(135deg, #00838f, #5e60ce);
    --gradient-secondary: linear-gradient(135deg, #2e7d32, #00838f);
    --gradient-tertiary: linear-gradient(135deg, #e76f51, #d6336c);
    --gradient-linear: linear-gradient(135deg, #00838f, #5e60ce);
    --gradient-tree: linear-gradient(135deg, #2e7d32, #00838f);
    --gradient-sorting: linear-gradient(135deg, #e76f51, #d6336c);
    --gradient-graph: linear-gradient(135deg, #5e60ce, #d6336c);

    /* Shadows & Glow */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.04);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 10px 18px rgba(0, 0, 0, 0.12);
    --shadow-glow: 0 0 16px rgba(0, 131, 143, 0.2);
    --glow-linear: 0 0 16px rgba(0, 131, 143, 0.2);
    --glow-tree: 0 0 16px rgba(46, 125, 50, 0.2);
    --glow-sorting: 0 0 16px rgba(231, 111, 81, 0.2);
    --glow-graph: 0 0 16px rgba(94, 96, 206, 0.2);

    /* Stripping Color */
    --bg-gradient-stripe-color: rgba(0, 0, 0, 0.03);
}

/* Scrollbar Styles */
::-webkit-scrollbar {
    height: 8px;
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-tertiary);
    border-radius: 0.375rem;
}

::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.15);
    border-radius: 0.375rem;
    transition: background 0.3s ease;
}

::-webkit-scrollbar-thumb:hover {
    background: rgba(255, 255, 255, 0.25);
}

[data-theme="light"] ::-webkit-scrollbar-thumb {
    background: rgba(0, 0, 0, 0.15)
}

[data-theme="light"] ::-webkit-scrollbar-thumb:hover {
    background: rgba(0, 0, 0, 0.25);
}

body {
    font-family: var(--font-sans);
    background: var(--bg-primary);
    color: var(--text-primary);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* Header Styles */
.main-header {
    background: var(--bg-secondary);
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
}

.main-header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 1.5rem;
}

.logo {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1.5rem;
    text-decoration: none;
}

.logo .logo-image {
    width: 70px;
    height: 70px;
}

.logo .logo-text h1
{
    background: var(--gradient-primary);
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 0.25rem;
}

.logo .logo-text span
{
    color: var(--text-secondary);
    display: block;
}

.main-nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 2rem;
}

.mobile-nav {
    display: none;
}

.nav-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 500;
    transition: 0.15s ease;
    position: relative;
}

.nav-link:hover,
.nav-link.active {
    color: var(--text-primary);
}

.nav-link::after {
    content: '';
    position: absolute;
    bottom: -4px;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--accent-cyan);
    transition: 0.15s ease;
}

.nav-link:hover::after,
.nav-link.active::after {
    width: 100%;
}

.theme-toggle {
    background: var(--bg-tertiary);
    border: 1px solid var(--bg-tertiary);
    border-radius: 0.5rem;
    padding: 0.5rem;
    color: var(--text-primary);
    cursor: pointer;
    font-size: 1rem;
    transition: 0.15s ease;
}

.theme-toggle:hover {
    background: var(--bg-secondary);
    transform: scale(1.05);
}

/* Hero Section Styles */
.hero-section
{
    text-align: center;
    margin-bottom: 4rem;
    padding: calc(80px + 4rem) 0 4rem;
}

.hero-content {
    max-width: 600px;
    margin: 0 auto;
}

.hero-title {
    font-size: clamp(2.5rem, 5vw, 3rem);
    font-weight: 700;
    margin-bottom: 1.5rem;
    background: var(--gradient-primary);
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle
{
    font-size: clamp(1.1rem, 2vw, 1.125rem);
    color: var(--text-secondary);
    margin-bottom: 3rem;
}

.hero-stats {
    display: flex;
    justify-content: center;
    gap: 3rem;
    margin-top: 3rem;
}

.stat {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 2rem;
    font-weight: 700;
    color: var(--accent-cyan);
    margin-bottom: 0.25rem;
}

.stat-label {
    color: var(--text-secondary);
}

/* Topics Section Styles */
.topics-section {
    padding: 4rem 0;
}

.section-title {
    font-size: 2.5rem;
    font-weight: 700;
    text-align: center;
    margin-bottom: 4rem;
    color: var(--text-primary);
}

.topic-category {
    margin-bottom: 4rem;
}

.category-title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 2rem;
    position: relative;
    padding-left: 1.5rem;
}

.category-title::before {
    content: '';
    position: absolute;
    left: 0;
    width: 4px;
    height: 100%;
    background: var(--accent-cyan);
    border-radius: 2px;
}

.topic-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
}

/* Topic Card Styles */
.topic-card {
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    background: var(--bg-secondary);
    border-radius: 0.75rem;
    padding: 2rem;
    text-decoration: none;
    transition: all 0.3s ease;
    position: relative;
}

.topic-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    transform: scaleX(0);
    transform-origin: left;
    transition: transform 0.3s ease;
}

.topic-card.topic-card:not(.coming-soon):hover::before {
    transform: scaleX(1);
}

.topic-card:not(.coming-soon):hover {
    background: var(--bg-tertiary);
    border-color: var(--accent-cyan);
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg), var(--shadow-glow);
}

.topic-card.linear::before { 
    background: var(--gradient-linear); 
}
.topic-card.tree::before { 
    background: var(--gradient-tree); 
}
.topic-card.sorting::before { 
    background: var(--gradient-sorting); 
}
.topic-card.graph::before { 
    background: var(--gradient-graph); 
}

.topic-card.linear:hover { 
    box-shadow: var(--shadow-lg), var(--glow-linear); 
}
.topic-card.tree:hover { 
    box-shadow: var(--shadow-lg), var(--glow-tree); 
}
.topic-card.sorting:hover { 
    box-shadow: var(--shadow-lg), var(--glow-sorting); 
}
.topic-card.graph:hover { 
    box-shadow: var(--shadow-lg), var(--glow-graph); 
}

.topic-card.coming-soon {
    opacity: 0.7;
    position: relative;
    cursor: not-allowed;
}

.topic-card.coming-soon::after {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: repeating-linear-gradient(45deg, transparent, transparent 10px, var(--bg-gradient-stripe-color) 10px, var(--bg-gradient-stripe-color) 20px);
}

.topic-card.coming-soon:hover {
    box-shadow: none;
}

.card-icon {
    font-size: 2rem;
    margin-bottom: 1.5rem;
}

.topic-card h4 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.topic-card p {
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    font-size: 0.875rem;
    line-height: 1.5;
}

.card-footer {
    display: flex;
    flex-direction: row;
    justify-content: space-between;
    align-items: center;
}

.difficulty,
.operations,
.complexity {
    background: var(--bg-primary);
    color: var(--accent-cyan);
    padding: 0.25rem 0.5rem;
    border-radius: 0.375rem;
    font-size: 0.75rem;
    border: 1px solid var(--accent-cyan);
}

.difficulty.easy {
    background: rgba(16, 185, 129, 0.2);
    color: var(--accent-green);
    border-color: var(--accent-green);
}

.difficulty.medium {
    background: rgba(234, 179, 8, 0.2);
    color: var(--accent-yellow);
    border-color: var(--accent-yellow);
}

.difficulty.hard {
    background: rgba(239, 68, 68, 0.2);
    color: var(--accent-red);
    border-color: var(--accent-red);
}

/* Footer Styles */
.main-footer{
    margin-top: 4rem;
    padding: 3rem 0;
    background: var(--bg-secondary);
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 3rem;
    margin-bottom: 3rem;
}

.footer-section h4 {
    margin-bottom: 1.5rem;
    color: var(--text-primary);
}

.footer-section p,
.footer-section a {
    color: var(--text-secondary);
    text-decoration: none;
    display: block;
    margin-bottom: 0.5rem;
}

.footer-section a:hover {
    color: var(--accent-cyan);
}

.footer-bottom {
    text-align: center;
    padding-top: 3rem;
    border-top: 1px solid var(--bg-tertiary);
    color: var(--text-muted);
}

/* Responsive Styles */
@media (max-width: 768px) {
    .container {
        padding: 0 1rem;
    }

    .logo .logo-image {
        width: 50px;
        height: 50px;
    }

    .logo .logo-text h1 {
        font-size: 1.5rem;
    }

    .logo .logo-text span {
        font-size: 0.875rem;
    }

    .main-header {
        padding: 0.5rem 1rem;
    }

    .main-nav {
        display: none;
    }

    .mobile-nav {
        display: flex;
        align-items: center;
        justify-content: space-between;
        gap: 2rem;
    }

    .menu-toggle {
        cursor: pointer;
        font-size: 1.5rem;
        border: none;
        background: var(--bg-secondary);
        color: var(--text-primary);
    }
    .mobile-menu {
        display: none;
        flex-direction: column;
        gap: 1rem;
        position: absolute;
        top: 80px;
        right: 0;
        background: var(--bg-secondary);
        padding: 1rem;
        border-radius: 0.5rem;
        box-shadow: var(--shadow-md);
    }

    .mobile-menu.open {
        display: flex;
    }

    .hero-title {
        font-size: 2rem;
    }
    
    .hero-stats {
        flex-direction: column;
        gap: 1.5rem;
    }
    
    .topic-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-content {
        grid-template-columns: 1fr;
        text-align: center;
    }
    
    .footer-links {
        flex-direction: column;
        gap: 1rem;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 1.75rem;
    }
    
    .topic-card {
        padding: 1.5rem;
    }
}