:root {
    
    --bg-primary: #0a0a0f;
    --bg-secondary: #111118;
    --bg-tertiary: #16161f;
    --bg-elevated: rgba(255, 255, 255, 0.03);
    --bg-glass: rgba(255, 255, 255, 0.06);
    --bg-glass-hover: rgba(255, 255, 255, 0.09);
    --bg-glass-active: rgba(255, 255, 255, 0.12);

    --text-primary: #f0f0f5;
    --text-secondary: #a0a0b0;
    --text-tertiary: #6e6e80;
    --text-muted: #4a4a5a;

    --accent-blue: #3b82f6;
    --accent-blue-light: #0055c5;
    --accent-purple: #0175e2;
    --accent-purple-light: #0779e4;
    --accent-cyan: #227aee;
    --accent-green: #34d399;
    --accent-yellow: #fbbf24;
    --accent-red: #f87171;
    --accent-orange: #fb923c;

    --border-subtle: rgba(255, 255, 255, 0.06);
    --border-medium: rgba(255, 255, 255, 0.1);
    --border-strong: rgba(255, 255, 255, 0.15);

    /* Gradients */
    --gradient-primary: linear-gradient(135deg, var(--accent-blue) 0%, var(--accent-purple) 100%);
    --gradient-text: linear-gradient(135deg, var(--accent-blue-light) 0%, var(--accent-purple-light) 50%, var(--accent-cyan) 100%);
    --gradient-glow: radial-gradient(circle at 50% 50%, rgba(59, 130, 246, 0.15) 0%, transparent 70%);

    /* Spacing Scale */
    --space-1: 0.25rem;
    --space-2: 0.5rem;
    --space-3: 0.75rem;
    --space-4: 1rem;
    --space-5: 1.25rem;
    --space-6: 1.5rem;
    --space-8: 2rem;
    --space-10: 2.5rem;
    --space-12: 3rem;
    --space-16: 4rem;
    --space-20: 5rem;
    --space-24: 6rem;
    --space-32: 8rem;

    /* Typography */
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;

    --text-xs: 0.75rem;
    --text-sm: 0.875rem;
    --text-base: 1rem;
    --text-lg: 1.125rem;
    --text-xl: 1.25rem;
    --text-2xl: 1.5rem;
    --text-3xl: 1.875rem;
    --text-4xl: 2.25rem;
    --text-5xl: 3rem;
    --text-6xl: 3.75rem;

    --font-light: 300;
    --font-normal: 400;
    --font-medium: 500;
    --font-semibold: 600;
    --font-bold: 700;
    --font-extrabold: 800;

    --leading-tight: 1.2;
    --leading-snug: 1.375;
    --leading-normal: 1.5;
    --leading-relaxed: 1.625;

    /* Layout */
    --container-max: 1280px;
    --container-padding: var(--space-6);
    --section-gap: var(--space-24);

    /* Effects */
    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    --radius-full: 9999px;

    --shadow-sm: 0 1px 2px rgba(27, 27, 27, 0.3);
    --shadow-md: 0 4px 12px rgba(56, 56, 56, 0.4);
    --shadow-lg: 0 8px 30px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 40px rgba(59, 130, 246, 0.15);

    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 400ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-bounce: 500ms cubic-bezier(0.34, 1.56, 0.64, 1);

    /* Z-index scale */
    --z-base: 1;
    --z-dropdown: 100;
    --z-sticky: 200;
    --z-modal: 300;
    --z-toast: 400;
}

/* ─── Reset & Base ─── */
*,
*::before,
*::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    text-rendering: optimizeLegibility;
}

body {
    font-family: var(--font-sans);
    font-size: var(--text-base);
    line-height: var(--leading-normal);
    color: var(--text-primary);
    background-color: var(--bg-primary);
    min-height: 100vh;
    overflow-x: hidden;
}

img,
svg,
video {
    display: block;
    max-width: 100%;
    height: auto;
}

a {
    color: inherit;
    text-decoration: none;
}

button {
    font-family: inherit;
    cursor: pointer;
    border: none;
    background: none;
    color: inherit;
}

ul,
ol {
    list-style: none;
}

input,
textarea,
select {
    font-family: inherit;
    font-size: inherit;
    color: inherit;
    background: none;
    border: none;
    outline: none;
}

pre,
code {
    font-family: var(--font-mono);
}

/* Selection */
::selection {
    background: rgba(0, 98, 255, 0.438);
    color: var(--text-primary);
}

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

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
}

::-webkit-scrollbar-thumb {
    background: var(--bg-tertiary);
    border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* Focus styles */
:focus-visible {
    outline: 2px solid var(--accent-blue);
    outline-offset: 2px;
    border-radius: var(--radius-sm);
}

/* ─── Ambient Background ─── */
.ambient-background {
    position: fixed;
    inset: 0;
    z-index: 0;
    pointer-events: none;
    overflow: hidden;
}

.orb {
    position: absolute;
    border-radius: 50%;
    filter: blur(80px);
    opacity: 0.4;
    animation: orbFloat 20s ease-in-out infinite;
}

.orb-1 {
    width: 600px;
    height: 600px;
    background: radial-gradient(circle, rgba(59, 130, 246, 0.3) 0%, transparent 70%);
    top: -200px;
    left: -100px;
    animation-delay: 0s;
}

.orb-2 {
    width: 500px;
    height: 500px;
    background: radial-gradient(circle, rgba(139, 92, 246, 0.25) 0%, transparent 70%);
    top: 40%;
    right: -150px;
    animation-delay: -7s;
}

.orb-3 {
    width: 400px;
    height: 400px;
    background: radial-gradient(circle, rgba(34, 146, 238, 0.404) 0%, transparent 70%);
    bottom: -100px;
    left: 30%;
    animation-delay: -14s;
}

@keyframes orbFloat {
    0%, 100% { transform: translate(0, 0) scale(1); }
    25% { transform: translate(30px, -30px) scale(1.05); }
    50% { transform: translate(-20px, 20px) scale(0.95); }
    75% { transform: translate(20px, 10px) scale(1.02); }
}

.noise-overlay {
    position: absolute;
    inset: 0;
    opacity: 0.03;
    background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noiseFilter)'/%3E%3C/svg%3E");
    background-repeat: repeat;
    background-size: 256px 256px;
}


.section-container {
    width: 100%;
    max-width: var(--container-max);
    margin: 0 auto;
    padding: 0 var(--container-padding);
    position: relative;
    z-index: var(--z-base);
}

/* ─── Glassmorphism Card ─── */
.glass-card {
    background: var(--bg-glass);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-lg);
    transition: transform var(--transition-base), box-shadow var(--transition-base), border-color var(--transition-base);
}

.glass-card:hover {
    border-color: var(--border-medium);
    box-shadow: var(--shadow-lg);
}

/* ─── Section Header Pattern ─── */
.section-header {
    text-align: center;
    max-width: 640px;
    margin: 0 auto var(--space-16);
}

.section-tag {
    display: inline-flex;
    align-items: center;
    gap: var(--space-2);
    font-size: var(--text-sm);
    font-weight: var(--font-medium);
    color: var(--accent-blue-light);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-4);
    padding: var(--space-2) var(--space-4);
    background: rgba(59, 130, 246, 0.1);
    border: 1px solid rgba(59, 130, 246, 0.15);
    border-radius: var(--radius-full);
}

.section-title {
    font-size: var(--text-4xl);
    font-weight: var(--font-bold);
    line-height: var(--leading-tight);
    letter-spacing: -0.02em;
    margin-bottom: var(--space-4);
    color: var(--text-primary);
}

.section-description {
    font-size: var(--text-lg);
    color: var(--text-secondary);
    line-height: var(--leading-relaxed);
}

.gradient-text {
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* ─── Buttons ─── */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-2);
    font-family: var(--font-sans);
    font-size: var(--text-base);
    font-weight: var(--font-semibold);
    padding: var(--space-3) var(--space-6);
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
    position: relative;
    overflow: hidden;
    white-space: nowrap;
}

.btn svg {
    flex-shrink: 0;
    transition: transform var(--transition-base);
}

.btn:hover svg {
    transform: translateX(2px);
}

.btn-primary {
    background: var(--gradient-primary);
    color: #fff;
    box-shadow: 0 4px 20px rgba(59, 130, 246, 0.3);
}

.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: 0 6px 24px rgba(59, 130, 246, 0.4);
}

.btn-primary:active {
    transform: translateY(0);
}

.btn-secondary {
    background: var(--bg-glass);
    color: var(--text-primary);
    border: 1px solid var(--border-medium);
    backdrop-filter: blur(10px);
}

.btn-secondary:hover {
    background: var(--bg-glass-hover);
    border-color: var(--border-strong);
    transform: translateY(-1px);
}

.btn-outline {
    background: transparent;
    color: var(--text-primary);
    border: 1px solid var(--border-medium);
}

.btn-outline:hover {
    background: var(--bg-glass);
    border-color: var(--border-strong);
}

.btn-ghost {
    background: transparent;
    color: var(--text-secondary);
}

.btn-ghost:hover {
    color: var(--text-primary);
}

.btn-large {
    padding: var(--space-4) var(--space-8);
    font-size: var(--text-lg);
}

/* ─── Navigation ─── */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: var(--z-sticky);
    padding: var(--space-4) 0;
    transition: background var(--transition-base), backdrop-filter var(--transition-base), box-shadow var(--transition-base);
}

.navbar.scrolled {
    background: rgba(10, 10, 15, 0.8);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    box-shadow: 0 1px 0 var(--border-subtle);
}

.nav-container {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: 0 var(--container-padding);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.nav-logo {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    font-weight: var(--font-bold);
    font-size: var(--text-xl);
    color: var(--text-primary);
    transition: opacity var(--transition-fast);
}

.nav-logo:hover {
    opacity: 0.8;
}

.logo-icon {
    flex-shrink: 0;
}

.nav-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    padding: var(--space-2);
    z-index: calc(var(--z-sticky) + 1);
}

.hamburger-line {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    border-radius: var(--radius-full);
    transition: transform var(--transition-base), opacity var(--transition-base);
}

.nav-toggle[aria-expanded="true"] .hamburger-line:nth-child(1) {
    transform: translateY(7px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .hamburger-line:nth-child(2) {
    opacity: 0;
}

.nav-toggle[aria-expanded="true"] .hamburger-line:nth-child(3) {
    transform: translateY(-7px) rotate(-45deg);
}

.nav-menu {
    display: flex;
    align-items: center;
    gap: var(--space-1);
}

.nav-link {
    display: block;
    padding: var(--space-2) var(--space-4);
    font-size: var(--text-sm);
    font-weight: var(--font-medium);
    color: var(--text-secondary);
    border-radius: var(--radius-md);
    transition: color var(--transition-fast), background var(--transition-fast);
}

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

/* ─── Footer ─── */
.footer {
    position: relative;
    z-index: var(--z-base);
    border-top: 1px solid var(--border-subtle);
    padding-top: var(--space-16);
    padding-bottom: var(--space-8);
}

.footer-container {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: 0 var(--container-padding);
    display: grid;
    grid-template-columns: 1fr 2fr;
    gap: var(--space-16);
    margin-bottom: var(--space-16);
}

.footer-brand {
    max-width: 320px;
}

.footer-logo {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    font-weight: var(--font-bold);
    font-size: var(--text-xl);
    margin-bottom: var(--space-4);
}

.footer-tagline {
    color: var(--text-secondary);
    line-height: var(--leading-relaxed);
    font-size: var(--text-sm);
}

.footer-nav {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-8);
}

.footer-nav-title {
    font-size: var(--text-sm);
    font-weight: var(--font-semibold);
    color: var(--text-primary);
    margin-bottom: var(--space-4);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.footer-nav-list {
    display: flex;
    flex-direction: column;
    gap: var(--space-3);
}

.footer-nav-list a {
    color: var(--text-secondary);
    font-size: var(--text-sm);
    transition: color var(--transition-fast);
}

.footer-nav-list a:hover {
    color: var(--text-primary);
}

.footer-bottom {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: 0 var(--container-padding);
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: var(--space-8);
    border-top: 1px solid var(--border-subtle);
}

.copyright {
    font-size: var(--text-sm);
    color: var(--text-tertiary);
}

.footer-made {
    font-size: var(--text-sm);
    color: var(--text-muted);
}

/* ─── Difficulty Badges ─── */
.difficulty-badge {
    display: inline-flex;
    align-items: center;
    padding: var(--space-1) var(--space-3);
    font-size: var(--text-xs);
    font-weight: var(--font-semibold);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    border-radius: var(--radius-full);
    border: 1px solid;
}

.difficulty-badge.easy {
    color: var(--accent-green);
    background: rgba(52, 211, 153, 0.1);
    border-color: rgba(52, 211, 153, 0.2);
}

.difficulty-badge.medium {
    color: var(--accent-yellow);
    background: rgba(251, 191, 36, 0.1);
    border-color: rgba(251, 191, 36, 0.2);
}

.difficulty-badge.hard {
    color: var(--accent-red);
    background: rgba(248, 113, 113, 0.1);
    border-color: rgba(248, 113, 113, 0.2);
}

/* ─── Tags ─── */
.tag {
    display: inline-flex;
    align-items: center;
    padding: var(--space-1) var(--space-2);
    font-size: var(--text-xs);
    font-weight: var(--font-medium);
    color: var(--text-tertiary);
    background: var(--bg-elevated);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-sm);
}

/* ─── Loading Spinner ─── */
.spinner {
    width: 20px;
    height: 20px;
    border: 2px solid var(--border-medium);
    border-top-color: var(--accent-blue);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* ─── Toast Notifications ─── */
.toast-container {
    position: fixed;
    bottom: var(--space-6);
    right: var(--space-6);
    z-index: var(--z-toast);
    display: flex;
    flex-direction: column;
    gap: var(--space-3);
    pointer-events: none;
}

.toast {
    pointer-events: all;
    padding: var(--space-4) var(--space-6);
    background: var(--bg-secondary);
    border: 1px solid var(--border-medium);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    display: flex;
    align-items: center;
    gap: var(--space-3);
    font-size: var(--text-sm);
    font-weight: var(--font-medium);
    animation: toastSlideIn var(--transition-bounce);
    max-width: 400px;
}

.toast.success {
    border-left: 3px solid var(--accent-green);
}

.toast.error {
    border-left: 3px solid var(--accent-red);
}

.toast.info {
    border-left: 3px solid var(--accent-blue);
}

@keyframes toastSlideIn {
    from {
        opacity: 0;
        transform: translateX(20px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

/* ─── Utility Classes ─── */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.hidden { display: none !important; }
.invisible { visibility: hidden; }

/* ─── Responsive Base ─── */
@media (max-width: 1024px) {
    :root {
        --text-4xl: 2rem;
        --text-5xl: 2.5rem;
        --text-6xl: 3rem;
        --section-gap: var(--space-20);
    }

    .footer-container {
        grid-template-columns: 1fr;
        gap: var(--space-10);
    }

    .footer-nav {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    :root {
        --container-padding: var(--space-4);
        --text-4xl: 1.75rem;
        --text-5xl: 2.25rem;
        --section-gap: var(--space-16);
    }

    .nav-toggle {
        display: flex;
    }

    .nav-menu {
        position: fixed;
        top: 0;
        right: 0;
        bottom: 0;
        width: 280px;
        background: var(--bg-secondary);
        border-left: 1px solid var(--border-subtle);
        flex-direction: column;
        align-items: flex-start;
        padding: calc(var(--space-16) + 20px) var(--space-6) var(--space-6);
        gap: var(--space-2);
        transform: translateX(100%);
        transition: transform var(--transition-base);
        z-index: var(--z-sticky);
    }

    .nav-menu.open {
        transform: translateX(0);
    }

    .nav-link {
        width: 100%;
        padding: var(--space-3) var(--space-4);
        font-size: var(--text-base);
    }

    .footer-nav {
        grid-template-columns: 1fr;
        gap: var(--space-6);
    }

    .footer-bottom {
        flex-direction: column;
        gap: var(--space-3);
        text-align: center;
    }

    .btn {
        width: 100%;
        justify-content: center;
    }
}

@media (max-width: 480px) {
    :root {
        --text-3xl: 1.5rem;
        --text-4xl: 1.5rem;
    }
}