/* ========== VARIABLES ========== */
:root {
  /* Colors */
  --primary: #3b82f6;
  --primary-hover: #2563eb;
  --bg-color: #f8fafc;
  --text-color: #1e293b;
  --card-bg: rgba(255, 255, 255, 0.9);
  --card-border: rgba(0, 0, 0, 0.1);
  --card-shadow: rgba(0, 0, 0, 0.1);

  /* Typography */
  --font-primary: "Inter", system-ui, -apple-system, sans-serif;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;
  --font-size-4xl: 2.5rem;
  --font-normal: 400;
  --font-medium: 500;
  --font-semibold: 600;
  --font-bold: 700;
  --line-height-tight: 1.2;
  --line-height-normal: 1.5;
  --line-height-relaxed: 1.75;

  /* Spacing & Layout */
  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 2rem;
  --spacing-lg: 4rem;
  --navbar-height: 4rem;
  --container-width: 1200px;
  --card-radius: 12px;

  /* Transitions */
  --transition-base: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);

  /* Z-index layers */
  --z-navbar: 1000;
  --z-mobile-menu: 1001;
  --z-overlay: 999;

  /* Shadow Effects */
  --shadow-sm: 0 2px 4px var(--card-shadow);
  --shadow-md: 0 4px 6px var(--card-shadow);
  --shadow-lg: 0 8px 20px var(--card-shadow);

  /* Common Effects */
  --hover-lift: translateY(-5px);
  --hover-lift-sm: translateY(-2px);

  /* Card Properties */
  --card-padding: var(--spacing-md);
}

/* ========== RESET & BASE ========== */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: var(--font-primary);
  background: var(--bg-color);
  color: var(--text-color);
  line-height: var(--line-height-normal);
  font-size: var(--font-size-base);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  transition: var(--transition-base);
}

/* ========== TYPOGRAPHY ========== */
h1,
h2,
h3,
h4,
h5,
h6 {
  font-weight: var(--font-bold);
  line-height: var(--line-height-tight);
  color: var(--text-color);
}

h1 {
  font-size: var(--font-size-4xl);
  margin-bottom: 1rem;
}

h2 {
  font-size: var(--font-size-3xl);
  margin-bottom: 0.75rem;
}

h3 {
  font-size: var(--font-size-xl);
  margin-bottom: 0.5rem;
}

/* ========== UTILITY CLASSES ========== */
.container {
  max-width: var(--container-width);
  margin: 0 auto;
  padding: 0 var(--spacing-md);
  width: 100%;
}

.flex-center,
.theme-toggle,
.social-links {
  display: flex;
  align-items: center;
}

.flex-center {
  justify-content: center;
}

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

.hover-lift {
  transition: var(--transition-base);
}

.hover-lift:hover,
.card-shadow-hover:hover,
.feature-card:hover,
.github-link:hover {
  transform: var(--hover-lift);
  box-shadow: var(--shadow-lg);
}

.card-shadow {
  box-shadow: var(--shadow-md);
}

.card-base {
  padding: var(--card-padding);
  border-radius: var(--card-radius);
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  transition: var(--transition-base);
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
}

/* ========== COMPONENTS ========== */

/* Skip Link */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background: var(--primary);
  color: white;
  padding: 8px;
  z-index: 100000;
  transition: top 0.1s ease-in;
}

.skip-link:focus {
  top: 0;
  outline: none;
}

/* Navbar & Navigation */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--navbar-height);
  background: var(--card-bg);
  background: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--card-border);
  z-index: var(--z-navbar);
}

.nav-container {
  height: 100%;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 var(--spacing-md);
  max-width: var(--container-width);
  margin: 0 auto;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: var(--font-size-lg);
  font-weight: var(--font-semibold);
  color: var(--text-color);
  text-decoration: none;
  z-index: 1001;
}

.nav-logo i {
  color: #f7df1e;
}

.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  color: var(--text-color);
  font-size: var(--font-size-xl);
  cursor: pointer;
  padding: var(--spacing-xs);
  z-index: var(--z-mobile-menu);
}

.nav-menu {
  display: flex;
  align-items: center;
  gap: var(--spacing-lg);
  margin-left: auto;
  padding: 0 var(--spacing-md);
  list-style: none;
}

.nav-link {
  position: relative;
  color: var(--text-color);
  text-decoration: none;
  font-weight: var(--font-medium);
  opacity: 0.8;
  transition: var(--transition-base);
  padding: var(--spacing-xs) var(--spacing-sm);
}

.nav-link::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--primary);
  transition: width 0.3s ease;
}

.nav-link:hover,
.nav-link.active {
  opacity: 1;
}

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

.github-link {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: var(--spacing-xs) var(--spacing-md);
  border-radius: var(--card-radius);
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  transition: var(--transition-base);
  margin-left: var(--spacing-md);
}

.mobile-menu-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  z-index: var(--z-overlay);
}

.mobile-menu-overlay.active {
  display: block;
}

/* Theme Toggle */
.theme-toggle {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 50%;
  width: 2.5rem;
  height: 2.5rem;
  padding: var(--spacing-xs);
  cursor: pointer;
  font-size: 1.5rem;
  transition: var(--transition-base);
  justify-content: center;
  box-shadow: var(--shadow-sm);
}

.theme-toggle:hover {
  transform: scale(1.1);
}

.theme-toggle:focus {
  outline: 2px solid var(--primary);
  border-radius: 4px;
}

/* Hero Section */
.hero {
  padding: 2rem 0;
  margin-top: var(--navbar-height);
  text-align: center;
  background: transparent;
}

.hero h1 {
  font-size: 2.75rem;
  font-weight: var(--font-bold);
  margin-bottom: 1rem;
  background: linear-gradient(135deg, var(--primary), var(--primary-hover));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  letter-spacing: -0.5px;
  transform: translateZ(0);
}

.hero-subtitle {
  font-size: 1.1rem;
  line-height: 1.5;
  color: var(--text-color);
  opacity: 1;
  max-width: 600px;
  margin: 0 auto 1.5rem;
  font-weight: var(--font-medium);
}

.hero-content {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
  max-width: 800px;
  margin: 0 auto;
}

.hero-actions {
  display: flex;
  gap: 0.75rem;
  justify-content: center;
  margin-top: 2rem;
}

.hero-badge {
  display: inline-block;
  padding: 0.5rem 1rem;
  background: rgba(59, 130, 246, 0.1);
  color: var(--primary);
  border-radius: 20px;
  font-size: 0.875rem;
  font-weight: 500;
  margin-bottom: 1.5rem;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  border-radius: var(--card-radius);
  font-weight: var(--font-medium);
  text-decoration: none;
  transition: var(--transition-base);
}

.btn-primary {
  background: var(--primary);
  color: white;
}

.btn-primary:hover {
  background: var(--primary-hover);
  transform: var(--hover-lift-sm);
}

.btn-secondary {
  background: var(--card-bg);
  color: var(--text-color);
  border: 1px solid var(--card-border);
}

.btn-secondary:hover {
  background: var(--bg-color);
  transform: var(--hover-lift-sm);
}

/* About Section */
.about-section {
  padding: 2.5rem 0;
  background: transparent;
  margin: 1rem 0;
}

.about-section h2 {
  text-align: center;
  margin-bottom: 1.5rem;
  font-size: 2.25rem;
  font-weight: var(--font-semibold);
}

.about-section p {
  max-width: 800px;
  margin: 0 auto 3rem;
  text-align: center;
  line-height: var(--line-height-relaxed);
  font-size: var(--font-size-lg);
  color: var(--text-color);
  opacity: 0.9;
}

/* Features Grid */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 2rem;
  margin: 3rem 0 4rem;
}

.feature-card {
  position: relative;
  text-align: center;
  padding: var(--card-padding);
  background: var(--card-bg);
  border-radius: var(--card-radius);
  border: 1px solid var(--card-border);
  box-shadow: var(--shadow-md);
  overflow: hidden;
  transition: var(--transition-base);
  will-change: transform, opacity;
}

.feature-card::before {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, transparent, var(--primary) 300%);
  opacity: 0;
  transition: opacity 0.3s ease;
}

.feature-card:hover::before {
  opacity: 0.1;
}

.feature-icon {
  position: relative;
  width: 48px;
  height: 48px;
  background: var(--card-bg);
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 1.5rem;
  transition: transform 0.3s ease;
  border: 1px solid var(--card-border);
}

.feature-card i {
  font-size: 2rem;
  color: var(--primary);
  margin-bottom: 1rem;
  filter: drop-shadow(0 0 8px rgba(59, 130, 246, 0.3));
}

.feature-card:hover i {
  transform: scale(1.1);
  color: var(--primary-hover);
  filter: drop-shadow(0 0 12px rgba(59, 130, 246, 0.4));
}

.feature-card h3 {
  position: relative;
  font-size: var(--font-size-xl);
  margin-bottom: 0.75rem;
  font-weight: var(--font-semibold);
}

.feature-card p {
  position: relative;
  font-size: var(--font-size-base);
  line-height: var(--line-height-normal);
  color: var(--text-color);
  opacity: 0.9;
}

/* Challenges Section */
.challenges-section {
  padding: 3rem 0;
  background: transparent;
}

.challenges-section h2 {
  text-align: center;
  margin-bottom: 3rem;
  font-size: 2rem;
}

.challenges-container {
  position: relative;
  min-height: 200px;
}

.challenges-container.loading::before {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 40px;
  height: 40px;
  margin: -20px 0 0 -20px;
  border: 4px solid rgba(59, 130, 246, 0.2);
  border-radius: 50%;
  border-top-color: var(--primary);
  animation: spin 0.8s linear infinite;
}

.challenges-grid {
  display: grid;
  gap: 2rem;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  padding: 1rem;
}

.challenges-grid a {
  background: var(--primary);
  padding: 2rem;
  border-radius: 12px;
  text-decoration: none;
  color: rgba(255, 255, 255, 0.95);
  text-align: center;
  box-shadow: var(--shadow-md);
  transition: var(--transition-base);
  border: 1px solid rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(5px);
  font-size: 1.1rem;
  line-height: 1.4;
  animation: fadeIn 0.4s ease-out forwards;
  animation-delay: calc(var(--index, 0) * 0.05s);
  text-shadow: 0 1px 2px rgba(0, 0, 0, 0.2);
  will-change: transform, opacity;
}

.challenges-grid a:hover {
  transform: var(--hover-lift);
  background: var(--primary-hover);
  border-color: rgba(255, 255, 255, 0.2);
}

/* Footer */
.footer {
  padding: var(--spacing-lg) 0 var(--spacing-md);
  background: var(--card-bg);
  border-top: 1px solid var(--card-border);
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-lg);
}

.footer-profile {
  display: flex;
  gap: var(--spacing-md);
  align-items: flex-start;
}

.author-image {
  width: 80px;
  height: 80px;
  border-radius: 50%;
  object-fit: cover;
  border: 2px solid var(--card-border);
}

.author-info h3 {
  font-size: var(--font-size-xl);
  margin-bottom: var(--spacing-xs);
}

.author-info p {
  font-size: var(--font-size-base);
  line-height: var(--line-height-normal);
  color: var(--text-color);
  opacity: 0.8;
  margin-bottom: var(--spacing-sm);
}

.social-links {
  justify-content: center;
  gap: 1.5rem;
  margin-top: 1rem;
}

.social-links a {
  color: var(--text-color);
  font-size: 1.5rem;
  transition: transform 0.3s ease;
  opacity: 0.8;
}

.social-links a:hover {
  transform: translateY(-3px);
  opacity: 1;
}

.footer-links h4 {
  font-size: var(--font-size-lg);
  margin-bottom: var(--spacing-sm);
  color: var(--text-color);
}

.footer-links nav {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
}

.footer-links a {
  color: var(--text-color);
  text-decoration: none;
  opacity: 0.8;
  transition: var(--transition-base);
}

.footer-links a:hover {
  opacity: 1;
  transform: translateX(5px);
}

.footer-bottom {
  padding-top: var(--spacing-md);
  border-top: 1px solid var(--card-border);
  text-align: center;
}

.footer-bottom p {
  color: var(--text-color);
  opacity: 0.8;
  font-size: var(--font-size-base);
}

/* ========== THEME MODES ========== */
[data-theme="dark"] {
  --bg-color: #0f172a;
  --text-color: #f1f5f9;
  --card-bg: rgba(30, 41, 59, 0.9);
  --card-border: rgba(255, 255, 255, 0.1);
  --card-shadow: rgba(0, 0, 0, 0.3);
}

[data-theme="dark"] .navbar {
  background: rgba(30, 41, 59, 0.9);
}

[data-theme="dark"] .challenges-grid a {
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.2);
}

[data-theme="dark"] .challenges-grid a:hover {
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.4);
}

[data-theme="dark"] .theme-toggle {
  color: var(--text-color);
}

[data-theme="dark"] .btn-secondary {
  color: var(--text-color);
  border-color: var(--primary);
}

[data-theme="dark"] .btn-secondary:hover {
  background: var(--primary);
  color: #ffffff;
}

[data-theme="dark"] .feature-card i {
  filter: drop-shadow(0 0 8px rgba(59, 130, 246, 0.5));
}

/* ========== FOCUS STATES ========== */
.nav-link:focus-visible,
.btn:focus-visible,
.github-link:focus-visible,
.mobile-menu-btn:focus-visible,
.footer-links a:focus-visible {
  outline: 3px solid var(--primary);
  outline-offset: 2px;
  text-decoration: underline;
}

/* ========== ANIMATIONS ========== */
@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

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

.animated {
  opacity: 0;
  transform: translateY(10px);
  transition: opacity 0.4s ease-out, transform 0.4s ease-out;
  will-change: transform, opacity;
}

.animated.animate {
  opacity: 1;
  transform: translateY(0);
}

/* For staggered animations */
.animated-delay-1 {
  transition-delay: 0.1s;
}
.animated-delay-2 {
  transition-delay: 0.2s;
}
.animated-delay-3 {
  transition-delay: 0.3s;
}
.animated-delay-4 {
  transition-delay: 0.4s;
}

/* ========== MEDIA QUERIES ========== */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  .animated {
    transition: none !important;
    animation: none !important;
    opacity: 1 !important;
    transform: none !important;
  }
}

@media (max-width: 768px) {
  :root {
    --spacing-md: 1.5rem;
    --spacing-lg: 3rem;
    --heading-size: 2rem;
  }

  /* Container */
  .container {
    padding: 0 var(--spacing-sm);
  }

  h1 {
    font-size: var(--font-size-3xl);
  }

  h2 {
    font-size: var(--font-size-2xl);
  }

  h3 {
    font-size: var(--font-size-xl);
  }

  /* Hero */
  .hero h1 {
    font-size: 2.25rem;
  }

  .hero-subtitle {
    font-size: 1rem;
    padding: 0 1rem;
  }

  /* Features */
  .features-grid {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }

  /* Navigation */
  .nav-menu {
    display: none;
    position: fixed;
    top: var(--navbar-height);
    left: 0;
    right: 0;
    padding: var(--spacing-md);
    background: var(--card-bg);
    flex-direction: column;
    gap: var(--spacing-md);
  }

  .nav-menu.active {
    display: flex;
    animation: slideIn 0.3s ease forwards;
    transform: translateZ(0);
  }

  .mobile-menu-btn {
    display: block;
  }

  .nav-link {
    width: 100%;
    text-align: center;
    padding: var(--spacing-sm);
  }

  .github-link {
    margin: 0;
    width: 100%;
    justify-content: center;
  }

  .footer {
    padding: var(--spacing-lg) var(--spacing-sm) var(--spacing-md);
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-md);
  }

  .footer-profile {
    flex-direction: column;
    align-items: center;
    text-align: center;
  }

  .social-links {
    justify-content: center;
  }

  .footer-links {
    text-align: center;
  }

  .footer-links nav {
    align-items: center;
  }

  .footer-links a:hover {
    transform: translateY(-2px);
  }

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

@media (max-width: 480px) {
  :root {
    --spacing-md: 1rem;
    --spacing-lg: 2rem;
  }

  .hero h1 {
    font-size: 1.75rem;
  }

  .hero-actions {
    flex-direction: column;
    gap: 1rem;
    width: 100%;
  }

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

  .challenges-grid {
    grid-template-columns: 1fr;
    gap: 1rem;
    padding: 0.5rem;
  }
}

@media (min-width: 769px) and (max-width: 1024px) {
  .features-grid {
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  }
}