/* Reset and base */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  /* Colors - WCAG AA compliant contrast ratios */
  --color-bg: #fafafa;
  --color-surface: #ffffff;
  --color-text: #1a1a1a;          /* 16.1:1 on white - passes AAA */
  --color-text-secondary: #4a4a4a; /* 7.0:1 on white - passes AA */
  --color-primary: #1d4ed8;        /* Darker blue for better contrast - 5.9:1 on white */
  --color-primary-hover: #1e40af;  /* Even darker for hover states */
  --color-border: #9ca3af;         /* Darker border for visibility - 2.7:1 on white */
  --color-focus: #2563eb;          /* Focus ring color */
  --color-shadow: rgba(0, 0, 0, 0.08);
  
  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-mono: 'Courier New', Courier, monospace;
  --font-size-base: 16px;
  --font-size-sm: 0.875rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;
  
  /* Spacing */
  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 1.5rem;
  --spacing-lg: 2rem;
  --spacing-xl: 3rem;
  
  /* Layout */
  --radius: 8px;
  --radius-lg: 12px;
  --max-width: 1200px;
  
  /* Focus */
  --focus-ring: 0 0 0 3px var(--color-focus);
  --focus-ring-offset: 0 0 0 2px var(--color-surface);
  
  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.2s ease;
}

body {
  font-family: var(--font-sans);
  font-size: var(--font-size-base);
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
}

/* Skip link for keyboard users */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background: var(--color-primary);
  color: white;
  padding: var(--spacing-xs) var(--spacing-sm);
  z-index: 1000;
  text-decoration: none;
  font-weight: 500;
  border-radius: 0 0 var(--radius) 0;
  transition: top var(--transition-fast);
}

.skip-link:focus {
  top: 0;
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

/* Focus styles for all interactive elements */
a:focus,
button:focus,
input:focus,
select:focus,
textarea:focus,
[tabindex]:focus {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

/* Remove default outline and use custom focus ring */
a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible,
[tabindex]:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
  box-shadow: var(--focus-ring);
}

/* Reduced motion preference */
@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;
  }
}

/* Visually hidden but accessible to screen readers */
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-md);
}

/* Header */
header {
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  padding: var(--spacing-md) 0;
  margin-bottom: var(--spacing-xl);
}

header .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
}

header h1 {
  font-size: var(--font-size-2xl);
  font-weight: 600;
}

header h1 a {
  color: var(--color-text);
  text-decoration: none;
}

header h1 a:hover,
header h1 a:focus-visible {
  color: var(--color-primary);
}

.tagline {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

nav {
  display: flex;
  gap: var(--spacing-sm);
  align-items: center;
}

nav a {
  color: var(--color-primary);
  text-decoration: none;
  font-size: var(--font-size-sm);
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: var(--radius);
  transition: background var(--transition-fast), color var(--transition-fast);
}

nav a:hover {
  text-decoration: underline;
  background: var(--color-bg);
}

nav a:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

/* Main content */
main {
  min-height: calc(100vh - 300px);
  padding-bottom: var(--spacing-xl);
}

/* Search section */
.search-section {
  margin-bottom: var(--spacing-lg);
}

.search-input {
  width: 100%;
  padding: var(--spacing-sm) var(--spacing-md);
  font-size: var(--font-size-base);
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-surface);
  color: var(--color-text);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.search-input:focus {
  outline: none;
  border-color: var(--color-focus);
  box-shadow: var(--focus-ring);
}

.search-input::placeholder {
  color: var(--color-text-secondary);
}

/* Ensure search works without JS - progressive enhancement */
.no-js .search-section {
  display: block;
}

/* Home page - courses grid */
.courses-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--spacing-md);
}

@media (min-width: 768px) {
  .courses-grid {
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  }
}

@media (min-width: 1024px) {
  .courses-grid {
    grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
  }
}

.course-card {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--spacing-md);
  transition: box-shadow var(--transition-normal), transform var(--transition-normal), border-color var(--transition-fast);
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xs);
}

.course-card:hover {
  box-shadow: 0 4px 12px var(--color-shadow);
  transform: translateY(-2px);
  border-color: var(--color-primary);
}

.course-card:focus-within {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

.course-cover {
  width: 100%;
  height: 160px;
  object-fit: cover;
  border-radius: var(--radius);
  margin-bottom: var(--spacing-xs);
}

.course-card h2 {
  font-size: var(--font-size-xl);
  margin-bottom: var(--spacing-xs);
}

.course-card h2 a {
  color: var(--color-text);
  text-decoration: none;
}

.course-card h2 a:hover,
.course-card h2 a:focus-visible {
  color: var(--color-primary);
}

.course-card p {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
  flex-grow: 1;
}

.course-meta {
  display: flex;
  gap: var(--spacing-sm);
  align-items: center;
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  flex-wrap: wrap;
  margin-top: var(--spacing-xs);
}

.tags {
  display: flex;
  gap: var(--spacing-xs);
  flex-wrap: wrap;
}

.tag {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  padding: 2px 8px;
  font-size: 0.75rem;
}

/* No results message */
.no-results {
  grid-column: 1 / -1;
  text-align: center;
  padding: var(--spacing-xl);
  color: var(--color-text-secondary);
  font-size: 1.1rem;
}

/* Course page */
.course {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--spacing-lg);
}

.course h1 {
  font-size: var(--font-size-3xl);
  margin-bottom: var(--spacing-sm);
}

.course-description {
  color: var(--color-text-secondary);
  font-size: var(--font-size-lg);
  margin-bottom: var(--spacing-md);
}

.course-meta {
  display: flex;
  gap: var(--spacing-sm);
  align-items: center;
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  flex-wrap: wrap;
}

.lessons {
  margin-top: var(--spacing-lg);
}

.lessons h2 {
  font-size: var(--font-size-2xl);
  margin-bottom: var(--spacing-md);
}

.lessons ul {
  list-style: none;
}

.lesson-item {
  background: var(--color-bg);
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--spacing-sm);
  margin-bottom: var(--spacing-sm);
  transition: border-color var(--transition-fast);
}

.lesson-item:hover {
  border-color: var(--color-primary);
}

.lesson-item a {
  color: var(--color-text);
  text-decoration: none;
  font-weight: 500;
  font-size: var(--font-size-base);
  display: block;
  padding: var(--spacing-xs);
  border-radius: var(--radius);
}

.lesson-item a:hover,
.lesson-item a:focus-visible {
  color: var(--color-primary);
  text-decoration: underline;
}

.lesson-item p {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
  margin-top: var(--spacing-xs);
}

/* Lesson page */
.lesson {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--spacing-lg);
}

.lesson h1 {
  font-size: var(--font-size-3xl);
  margin-bottom: var(--spacing-lg);
}

.lesson-content {
  line-height: 1.8;
}

.lesson-content h2 {
  font-size: var(--font-size-2xl);
  margin-top: var(--spacing-lg);
  margin-bottom: var(--spacing-sm);
}

.lesson-content h3 {
  font-size: var(--font-size-xl);
  margin-top: var(--spacing-md);
  margin-bottom: var(--spacing-sm);
}

.lesson-content p {
  margin-bottom: var(--spacing-sm);
}

.lesson-content ul,
.lesson-content ol {
  margin-bottom: var(--spacing-sm);
  padding-left: var(--spacing-md);
}

.lesson-content li {
  margin-bottom: var(--spacing-xs);
}

.lesson-content code {
  background: var(--color-bg);
  padding: 2px 6px;
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 0.9em;
}

.lesson-content pre {
  background: var(--color-bg);
  padding: var(--spacing-sm);
  border-radius: var(--radius);
  overflow-x: auto;
  margin-bottom: var(--spacing-sm);
}

.lesson-content pre code {
  background: none;
  padding: 0;
}

.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: var(--spacing-xl);
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--color-border);
  gap: var(--spacing-sm);
  flex-wrap: wrap;
}

.lesson-nav a {
  color: var(--color-primary);
  text-decoration: none;
  padding: var(--spacing-xs) var(--spacing-sm);
  border: 2px solid var(--color-border);
  border-radius: var(--radius);
  transition: background var(--transition-fast), border-color var(--transition-fast), color var(--transition-fast);
  font-weight: 500;
}

.lesson-nav a:hover,
.lesson-nav a:focus-visible {
  background: var(--color-bg);
  border-color: var(--color-primary);
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

.nav-back {
  color: var(--color-text-secondary);
  border-style: dashed;
}

/* Footer */
footer {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding: var(--spacing-md) 0;
  margin-top: var(--spacing-xl);
  text-align: center;
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

/* Responsive breakpoints */
/* Mobile first - base styles */
@media (max-width: 480px) {
  :root {
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
  }
  
  .container {
    padding: 0 var(--spacing-sm);
  }
  
  header h1 {
    font-size: var(--font-size-xl);
  }
  
  .tagline {
    width: 100%;
    order: 2;
  }
  
  nav {
    width: 100%;
    justify-content: center;
    order: 3;
  }
  
  .courses-grid {
    grid-template-columns: 1fr;
  }
  
  .lesson-nav {
    flex-direction: column;
  }
  
  .lesson-nav a {
    width: 100%;
    text-align: center;
  }
  
  .course h1,
  .lesson h1 {
    font-size: var(--font-size-2xl);
  }
}

/* Tablet */
@media (min-width: 481px) and (max-width: 767px) {
  .container {
    padding: 0 var(--spacing-md);
  }
  
  .courses-grid {
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  }
}

/* Desktop */
@media (min-width: 768px) {
  .courses-grid {
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  }
}

/* Large desktop */
@media (min-width: 1024px) {
  .courses-grid {
    grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
  }
}

/* Print styles */
@media print {
  header,
  footer,
  .search-section,
  .lesson-nav {
    display: none;
  }
  
  body {
    background: white;
    color: black;
  }
  
  .container {
    max-width: none;
    padding: 0;
  }
  
  .course,
  .lesson {
    border: none;
    padding: 0;
  }
}