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

:root {
  --primary: #667eea;
  --primary-dark: #764ba2;
  --secondary: #f093fb;
  --dark: #1a1a2e;
  --dark-light: #16213e;
  --light: #e8f5f0;
  --white: #ffffff;
  --shadow: rgba(0, 0, 0, 0.1);
  --shadow-dark: rgba(0, 0, 0, 0.3);
  --gradient: linear-gradient(
    135deg,
    var(--primary) 0%,
    var(--primary-dark) 100%
  );
  --gradient-secondary: linear-gradient(
    135deg,
    var(--secondary) 0%,
    var(--primary) 100%
  );
}

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(135deg, #77d09e 0%, #9b6ec8 100%);
  min-height: 100vh;
  color: var(--dark);
  overflow-x: hidden;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem;
}

.header {
  text-align: center;
  margin-bottom: 3rem;
  animation: fadeInDown 1s ease-out;
}

.header h1 {
  font-size: 3.5rem;
  color: var(--white);
  margin-bottom: 1rem;
  text-shadow: 0 4px 8px var(--shadow-dark);
  font-weight: 700;
}

.header p {
  font-size: 1.2rem;
  color: rgba(255, 255, 255, 0.9);
  max-width: 600px;
  margin: 0 auto;
  line-height: 1.6;
}

.navigation-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 2rem;
  margin-bottom: 3rem;
}

.nav-card {
  background: var(--white);
  border-radius: 20px;
  padding: 2rem;
  box-shadow: 0 10px 30px var(--shadow);
  transition: all 0.3s ease;
  position: relative;
  overflow: hidden;
  text-decoration: none;
  color: inherit;
  animation: fadeInUp 0.8s ease-out;
  animation-fill-mode: both;
}

.nav-card:hover {
  transform: translateY(-10px);
  box-shadow: 0 20px 40px var(--shadow-dark);
}

.nav-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--gradient);
  border-radius: 20px 20px 0 0;
}

.nav-card.fundamentals::before {
  background: linear-gradient(90deg, #4facfe 0%, #00f2fe 100%);
}

.nav-card.dsa::before {
  background: linear-gradient(90deg, #43e97b 0%, #38f9d7 100%);
}

.nav-card.competitive::before {
  background: linear-gradient(90deg, #fa709a 0%, #fee140 100%);
}

.nav-card.web::before {
  background: linear-gradient(90deg, #a8edea 0%, #fed6e3 100%);
}

.nav-card.utility::before {
  background: linear-gradient(90deg, #ff9a9e 0%, #fecfef 100%);
}

.nav-card.docs::before {
  background: linear-gradient(90deg, #ffecd2 0%, #fcb69f 100%);
}

.nav-card.reallife::before {
  background: linear-gradient(90deg, #ff8a80 0%, #ea80fc 100%);
}

.nav-icon {
  font-size: 3rem;
  margin-bottom: 1rem;
  display: block;
}

.nav-card h3 {
  font-size: 1.5rem;
  margin-bottom: 1rem;
  color: var(--dark);
  font-weight: 600;
}

.nav-card p {
  color: #666;
  line-height: 1.6;
  margin-bottom: 1rem;
}

.nav-card .folder-path {
  font-family: "Courier New", monospace;
  font-size: 0.9rem;
  color: var(--primary);
  background: rgba(102, 126, 234, 0.1);
  padding: 0.5rem;
  border-radius: 8px;
  margin-top: 1rem;
}

.stats-section {
  background: rgba(255, 255, 255, 0.95);
  border-radius: 20px;
  padding: 2rem;
  margin-bottom: 2rem;
  backdrop-filter: blur(10px);
  animation: fadeIn 1.2s ease-out;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 1rem;
  text-align: center;
}

.stat-item {
  padding: 1rem;
}

.stat-number {
  font-size: 2rem;
  font-weight: bold;
  color: var(--primary);
  display: block;
}

.stat-label {
  color: #666;
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: 1px;
}

.footer {
  text-align: center;
  color: rgba(255, 255, 255, 0.8);
  margin-top: 3rem;
}

.footer a {
  color: var(--white);
  text-decoration: none;
  font-weight: 500;
}

.footer a:hover {
  text-decoration: underline;
}

/* Animations */
@keyframes fadeInDown {
  from {
    opacity: 0;
    transform: translateY(-30px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeIn {
  from {
    opacity: 0;
  }

  to {
    opacity: 1;
  }
}

/* Animation delays */
.nav-card:nth-child(1) {
  animation-delay: 0.1s;
}

.nav-card:nth-child(2) {
  animation-delay: 0.2s;
}

.nav-card:nth-child(3) {
  animation-delay: 0.3s;
}

.nav-card:nth-child(4) {
  animation-delay: 0.4s;
}

.nav-card:nth-child(5) {
  animation-delay: 0.5s;
}

.nav-card:nth-child(6) {
  animation-delay: 0.6s;
}

.nav-card:nth-child(7) {
  animation-delay: 0.7s;
}

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

  .header h1 {
    font-size: 2.5rem;
  }

  .navigation-grid {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }

  .nav-card {
    padding: 1.5rem;
  }

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

@media (max-width: 480px) {
  .header h1 {
    font-size: 2rem;
  }

  .nav-icon {
    font-size: 2.5rem;
  }
}

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

/* File Sections */
.files-section {
  background: rgba(255, 255, 255, 0.95);
  border-radius: 20px;
  padding: 2rem;
  margin-bottom: 3rem;
  backdrop-filter: blur(10px);
  animation: fadeIn 0.8s ease-out;
  scroll-margin-top: 2rem;
}

.section-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 2rem;
  padding-bottom: 1rem;
  border-bottom: 3px solid var(--primary);
}

.section-header h2 {
  margin: 0;
  font-size: 2rem;
  color: var(--primary);
}

.back-to-top {
  background: var(--gradient);
  color: white;
  padding: 0.5rem 1rem;
  border-radius: 10px;
  text-decoration: none;
  font-weight: 600;
  transition: all 0.3s ease;
  box-shadow: 0 4px 15px var(--shadow);
}

.back-to-top:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px var(--shadow-dark);
}

.file-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 1rem;
}

.file-card {
  background: #f8f9fa;
  border: 1px solid #e9ecef;
  border-radius: 10px;
  padding: 1rem;
  transition: all 0.3s ease;
  text-decoration: none;
  color: inherit;
  display: block;
}

.file-card:hover {
  background: #e9ecef;
  transform: translateY(-2px);
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
}

.file-icon {
  font-size: 2rem;
  margin-bottom: 0.5rem;
  display: block;
}

.file-name {
  font-weight: 600;
  font-size: 0.9rem;
  margin-bottom: 0.5rem;
  color: var(--primary);
}

.file-path {
  font-size: 0.8rem;
  color: #666;
  font-family: "Courier New", monospace;
  background: rgba(102, 126, 234, 0.1);
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
}

@keyframes slideIn {
  from {
    transform: translateY(-30px);
    opacity: 0;
  }

  to {
    transform: translateY(0);
    opacity: 1;
  }
}

/* Dark mode toggle (optional) */
.theme-toggle {
  position: fixed;
  top: 20px;
  right: 20px;
  background: rgba(255, 255, 255, 0.2);
  border: none;
  border-radius: 50%;
  width: 50px;
  height: 50px;
  color: white;
  font-size: 1.2rem;
  cursor: pointer;
  backdrop-filter: blur(10px);
  transition: all 0.3s ease;
}

.theme-toggle:hover {
  background: rgba(255, 255, 255, 0.3);
  transform: scale(1.1);
}