:root {
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --radius-md: 12px;
  --radius-lg: 18px;
  --color-primary: #306998;
  --color-primary-dark: #264969;
  --color-bg: #fff;
  --color-bg-alt: #f6f8fa;
  --color-text-main: #223b55;
  --color-text-secondary: #46628a;
  --shadow-md: 0 4px 16px rgba(38, 70, 105, 0.11);
  --shadow-lg: 0 8px 26px rgba(38, 70, 105, 0.15);
}

body {
  background: var(--color-bg);
  color: var(--color-text-main);
  font-family: 'Poppins', Arial, sans-serif;
  line-height: 1.7;
  margin: 0;
  min-height: 100vh;
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color 0.3s;
}

a:hover {
  color: var(--color-primary-dark);
}

.header {
  background: linear-gradient(90deg, var(--color-primary) 70%, var(--color-primary-dark) 100%);
  color: #fff;
  padding: var(--space-4) var(--space-6);
  box-shadow: var(--shadow-md);
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  position: relative;
}

.logo h1 {
  font-size: 2rem;
  font-weight: 700;
  color: #fff;
  text-shadow: 0 2px 8px rgba(38,105,152,0.12);
  letter-spacing: 1.5px;
  margin: 0;
}

.nav ul {
  list-style: none;
  display: flex;
  gap: var(--space-6);
  margin: 0;
  padding: 0;
}

.nav a {
  font-weight: 600;
  color: #fff;
  border-bottom: 2px solid transparent;
  transition: color 0.2s, border-bottom 0.2s;
  padding: var(--space-2) 0;
}

.nav a.active,
.nav a:hover {
  border-color: #fff;
  color: #fff;
}

.mobile-menu-btn {
  display: none;
  flex-direction: column;
  gap: 6px;
  background: none;
  border: none;
  cursor: pointer;
  z-index: 101;
  padding: var(--space-2);
}

.mobile-menu-btn span {
  width: 28px;
  height: 4px;
  background: #fff;
  border-radius: 2px;
  transition: all 0.3s ease;
}

.mobile-menu-btn.active span:nth-child(1) { 
  transform: rotate(45deg) translate(7px, 7px);
}
.mobile-menu-btn.active span:nth-child(2) { 
  opacity: 0;
}
.mobile-menu-btn.active span:nth-child(3) { 
  transform: rotate(-45deg) translate(7px, -7px);
}

.hero {
  background: var(--color-bg-alt);
  min-height: 360px;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  padding: 4rem 2rem 3rem;
}

.hero-content {
  flex: 1 1 340px;
  max-width: 560px;
}

.hero-title {
  font-size: 2.7rem;
  font-weight: 700;
  color: var(--color-primary-dark);
  margin-bottom: 0.9rem;
  letter-spacing: 1.5px;
  line-height: 1.2;
}

.highlight { 
  color: var(--color-primary);
}

.hero-subtitle {
  font-size: 1.12rem;
  color: var(--color-text-secondary);
  margin-bottom: 2rem;
  max-width: 480px;
  line-height: 1.6;
}

.cta-button {
  background: var(--color-primary);
  color: #fff;
  padding: 0.85rem 2.1rem;
  font-weight: 700;
  font-size: 1.09rem;
  border-radius: var(--radius-lg);
  border: none;
  box-shadow: var(--shadow-md);
  letter-spacing: 1px;
  cursor: pointer;
  transition: background 0.22s, color 0.22s, box-shadow 0.22s;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.cta-button:hover {
  background: var(--color-primary-dark);
  color: #f6f8fa;
  box-shadow: var(--shadow-lg);
}

.hero-image {
  flex: 1 1 300px;
  margin-top: 2rem;
}

.code-snippet {
  background: var(--color-primary-dark);
  color: #fff;
  padding: 1.4rem 1.7rem;
  border-radius: var(--radius-lg);
  font-family: 'Fira Code', monospace;
  font-size: 1rem;
  overflow-x: auto;
  box-shadow: var(--shadow-md);
  border-left: 8px solid var(--color-primary);
  line-height: 1.5;
}

.features {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: var(--space-6);
  padding: 3rem 2rem;
  background: #fff;
}

.feature {
  background: var(--color-bg-alt);
  padding: var(--space-4);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  text-align: center;
  transition: transform 0.23s, box-shadow 0.25s;
}

.feature:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-5px);
}

.feature-icon {
  font-size: 2.2rem;
  margin-bottom: var(--space-3);
  color: var(--color-primary);
}

.feature h3 {
  font-size: 1.2rem;
  margin-bottom: 0.5rem;
  color: var(--color-primary-dark);
  line-height: 1.3;
}

.feature p {
  line-height: 1.5;
}

.preview {
  padding: 3rem 2rem;
  background: var(--color-bg-alt);
  text-align: center;
}

.preview h2 {
  font-weight: 700;
  font-size: 2rem;
  color: var(--color-primary-dark);
  margin-bottom: 2rem;
  line-height: 1.3;
}

.topics-preview {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: var(--space-5);
}

.topic-card {
  background: #fff;
  padding: 1.25rem;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  transition: transform 0.24s, box-shadow 0.27s;
}

.topic-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.topic-card h3 {
  color: var(--color-primary-dark);
  margin-bottom: 0.6rem;
  line-height: 1.3;
}

.topic-card p {
  color: var(--color-text-secondary);
  line-height: 1.5;
}

.secondary-button {
  display: inline-block;
  margin-top: var(--space-6);
  padding: 0.7rem 1.6rem;
  border-radius: var(--radius-md);
  font-weight: 600;
  font-size: 1rem;
  color: var(--color-primary-dark);
  border: 2px solid var(--color-primary);
  background: transparent;
  cursor: pointer;
  transition: background 0.2s, color 0.2s;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.secondary-button:hover {
  background: var(--color-primary-dark);
  color: #fff;
}

.footer {
  background: var(--color-primary-dark);
  color: #dde6f3;
  padding: 3rem 2rem;
  font-size: 0.96rem;
}

.footer-content {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: var(--space-6);
}

.footer-logo h2 {
  color: #fff;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.footer-logo p {
  color: #b7c4d3;
  font-style: italic;
  line-height: 1.5;
}

.footer-links h3,
.footer-social h3 {
  color: #fff;
  margin-bottom: var(--space-3);
  font-weight: 600;
}

.footer-links ul {
  list-style: none;
  margin: 0; 
  padding: 0;
}

.footer-links li { 
  margin: 0.3rem 0; 
}

.footer-links a {
  color: #dde6f3;
  transition: color 0.18s;
  padding: var(--space-1) 0;
  display: inline-block;
}

.footer-links a:hover {
  color: #fff;
}

.social-icons {
  display: flex;
  gap: var(--space-4);
  margin-top: 0.5rem;
}

.social-icon {
  min-height: 44px;
  min-width: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.social-icon svg {
  stroke: #dde6f3;
  transition: stroke 0.21s;
  width: 24px; 
  height: 24px;
}

.social-icon:hover svg {
  stroke: #fff;
}

.footer-bottom {
  text-align: center;
  margin-top: var(--space-6);
  border-top: 1px solid #1a283c;
  padding-top: var(--space-3);
  color: #b7c4d3;
  line-height: 1.5;
}

/* Responsive Design */
@media (max-width: 1024px) {
  .hero {
    padding: 3rem 1.5rem 2rem;
  }
  
  .features {
    padding: 2.5rem 1.5rem;
    gap: var(--space-5);
  }
  
  .preview {
    padding: 2.5rem 1.5rem;
  }
}

@media (max-width: 768px) {
  .mobile-menu-btn { 
    display: flex; 
  }
  
  .header {
    padding: var(--space-3) var(--space-4);
  }
  
  .logo h1 {
    font-size: 1.6rem;
    letter-spacing: 1px;
  }
  
  .nav { 
    position: fixed;
    top: 0; 
    right: 0;
    background: var(--color-primary);
    height: 100vh;
    width: 85vw;
    max-width: 300px;
    flex-direction: column;
    padding: 5rem 1rem 1rem;
    transform: translateX(100%);
    transition: transform 0.33s;
    opacity: 0; 
    visibility: hidden; 
    z-index: 100;
    box-shadow: -5px 0 15px rgba(0,0,0,0.1);
  }
  
  .nav.nav-open {
    transform: translateX(0);
    opacity: 1;
    visibility: visible;
  }
  
  .nav ul { 
    flex-direction: column; 
    gap: var(--space-4);
    width: 100%;
  }
  
  .nav a { 
    font-size: 1.2rem; 
    color: #fff;
    padding: var(--space-3) var(--space-4);
    border-radius: var(--radius-md);
    width: 100%;
    text-align: left;
    min-height: 44px;
    display: flex;
    align-items: center;
  }
  
  .nav a:hover {
    background: rgba(255,255,255,0.1);
  }
  
  .hero {
    flex-direction: column;
    text-align: center;
    padding: 2rem 1rem;
    min-height: auto;
  }
  
  .hero-title {
    font-size: 2rem;
    margin-bottom: 1rem;
  }
  
  .hero-subtitle {
    font-size: 1.05rem;
    margin-bottom: 1.5rem;
  }
  
  .hero-image {
    margin-top: 1.5rem;
    width: 100%;
  }
  
  .code-snippet {
    padding: 1rem;
    font-size: 0.9rem;
    margin-top: 1rem;
  }
  
  .features {
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    padding: 2rem 1rem;
    gap: var(--space-4);
  }
  
  .feature {
    padding: var(--space-3);
  }
  
  .feature h3 {
    font-size: 1.1rem;
  }
  
  .preview {
    padding: 2rem 1rem;
  }
  
  .preview h2 {
    font-size: 1.6rem;
    margin-bottom: 1.5rem;
  }
  
  .topics-preview {
    grid-template-columns: 1fr;
    gap: var(--space-4);
  }
  
  .topic-card {
    padding: 1rem;
  }
  
  .footer {
    padding: 2rem 1rem;
  }
  
  .footer-content {
    flex-direction: column;
    gap: var(--space-4);
    text-align: center;
  }
  
  .social-icons {
    justify-content: center;
  }
}

@media (max-width: 480px) {
  .header {
    padding: var(--space-2) var(--space-3);
  }
  
  .logo h1 {
    font-size: 1.4rem;
  }
  
  .nav {
    width: 90vw;
    padding: 4rem 0.5rem 1rem;
  }
  
  .nav a {
    font-size: 1.1rem;
    padding: var(--space-2) var(--space-3);
  }
  
  .hero {
    padding: 1.5rem 0.75rem;
  }
  
  .hero-title { 
    font-size: 1.6rem;
    line-height: 1.2;
  }
  
  .hero-subtitle {
    font-size: 1rem;
  }
  
  .cta-button {
    padding: 0.75rem 1.5rem;
    font-size: 1rem;
    width: 100%;
    max-width: 280px;
  }
  
  .code-snippet {
    padding: 0.75rem;
    font-size: 0.85rem;
  }
  
  .features { 
    grid-template-columns: 1fr; 
    gap: var(--space-3);
    padding: 1.5rem 0.75rem;
  }
  
  .feature {
    padding: var(--space-3);
  }
  
  .feature-icon {
    font-size: 1.8rem;
  }
  
  .feature h3 {
    font-size: 1rem;
  }
  
  .preview {
    padding: 1.5rem 0.75rem;
  }
  
  .preview h2 {
    font-size: 1.4rem;
  }
  
  .topic-card {
    padding: 0.75rem;
  }
  
  .secondary-button {
    width: 100%;
    max-width: 280px;
    padding: 0.75rem 1rem;
  }
  
  .footer {
    padding: 1.5rem 0.75rem;
    font-size: 0.9rem;
  }
  
  .footer-links a {
    padding: var(--space-2) 0;
  }
}

/* Touch-friendly improvements */
@media (max-width: 768px) {
  /* Disable hover effects on touch devices */
  .feature:hover,
  .topic-card:hover {
    transform: none;
  }
  
  /* Add active states for better touch feedback */
  .feature:active,
  .topic-card:active {
    transform: scale(0.98);
    transition: transform 0.1s;
  }
  
  .cta-button:active,
  .secondary-button:active {
    transform: scale(0.95);
    transition: transform 0.1s;
  }
}

/* Improved text readability on small screens */
@media (max-width: 480px) {
  body {
    line-height: 1.6;
  }
  
  .hero-title,
  .preview h2,
  .feature h3 {
    line-height: 1.3;
  }
  
  .hero-subtitle,
  .feature p,
  .topic-card p {
    line-height: 1.5;
  }
}