:root {
  /* Modern HSL Color Palette */
  --color-primary: hsl(15, 87%, 55%); /* Strava-like orange */
  --color-primary-dark: hsl(15, 87%, 45%);
  --color-secondary: hsl(220, 90%, 56%);
  
  /* Backgrounds & Surfaces */
  --bg-body: hsl(220, 20%, 97%);
  --bg-surface: hsl(0, 0%, 100%);
  --bg-surface-elevated: hsl(0, 0%, 100%);
  
  /* Text */
  --text-main: hsl(220, 30%, 15%);
  --text-muted: hsl(220, 15%, 45%);
  
  /* Borders and elements */
  --border-light: hsl(220, 20%, 90%);
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  
  /* Radii */
  --radius-md: 0.5rem;
  --radius-lg: 1rem;
  --radius-full: 9999px;
  
  /* Transitions */
  --transition-fast: 150ms ease-in-out;
  --transition-normal: 250ms ease;
}

/* Dark Mode Query */
@media (prefers-color-scheme: dark) {
  :root {
    --bg-body: hsl(220, 20%, 8%);
    --bg-surface: hsl(220, 20%, 12%);
    --bg-surface-elevated: hsl(220, 20%, 16%);
    
    --text-main: hsl(220, 20%, 95%);
    --text-muted: hsl(220, 15%, 70%);
    
    --border-light: hsl(220, 20%, 20%);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.3);
  }
}

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

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background-color: var(--bg-body);
  color: var(--text-main);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

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

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

/* Base Layout */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1rem;
}

/* Navbar */
.navbar {
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border-light);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow-sm);
}

.navbar-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 4rem;
}

.navbar-brand {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--color-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.navbar-menu {
  display: flex;
  gap: 1.5rem;
  align-items: center;
}

/* Cards */
.card {
  background-color: var(--bg-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border-light);
  overflow: hidden;
  transition: transform var(--transition-normal), box-shadow var(--transition-normal);
}

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

.card-header {
  padding: 1.5rem;
  border-bottom: 1px solid var(--border-light);
}

.card-body {
  padding: 1.5rem;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.5rem 1rem;
  font-weight: 500;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all var(--transition-fast);
  font-size: 0.95rem;
}

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

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

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

.btn-outline:hover {
  background-color: var(--bg-surface-elevated);
}

/* Strava specific */
.btn-strava {
  background-color: #fc4c02;
  color: white;
  font-weight: 600;
  border-radius: var(--radius-md);
}

.btn-strava:hover {
  background-color: #e34402;
  color: white;
}

/* Typography */
h1, h2, h3, h4 {
  color: var(--text-main);
  line-height: 1.2;
}

.text-muted {
  color: var(--text-muted);
}

/* Utilities */
.mt-4 { margin-top: 1rem; }
.mb-4 { margin-bottom: 1rem; }
.py-8 { padding-top: 2rem; padding-bottom: 2rem; }
.text-center { text-align: center; }
.flex-center { display: flex; justify-content: center; align-items: center; }

/* Challenge page layout helpers */
.challenge-stats-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

.challenge-main-grid {
  display: grid;
  grid-template-columns: 1fr 350px;
  gap: 2rem;
}

.attempt-summary-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

.table-scroll {
  width: 100%;
  overflow-x: auto;
}

/* Responsive breakpoints */
@media (max-width: 960px) {
  .challenge-main-grid {
    grid-template-columns: 1fr;
    gap: 1rem;
  }

  .challenge-stats-grid,
  .attempt-summary-grid {
    grid-template-columns: 1fr;
  }

  .card[style*="position: sticky"] {
    position: static !important;
  }
}

@media (max-width: 720px) {
  .navbar-container {
    height: auto;
    padding-top: 0.75rem;
    padding-bottom: 0.75rem;
    flex-wrap: wrap;
    gap: 0.75rem;
  }

  .navbar-menu {
    width: 100%;
    justify-content: flex-start;
    flex-wrap: wrap;
    gap: 0.5rem;
  }

  .card-header,
  .card-body {
    padding: 1rem;
  }
}

@media (max-width: 420px) {
  .table-scroll {
    overflow-x: visible;
  }

  .responsive-table {
    min-width: 0 !important;
    width: 100% !important;
  }

  .responsive-table thead {
    display: none;
  }

  .responsive-table tbody,
  .responsive-table tr,
  .responsive-table td {
    display: block;
    width: 100%;
  }

  .responsive-table tr {
    border: 1px solid var(--border-light);
    border-radius: var(--radius-md);
    margin-bottom: 0.75rem;
    padding: 0.5rem;
    background: var(--bg-surface-elevated);
  }

  .responsive-table td {
    text-align: left !important;
    padding: 0.3rem 0 !important;
    border: 0 !important;
    font-size: 0.9rem;
  }

  .responsive-table td::before {
    content: attr(data-label) ": ";
    color: var(--text-muted);
    font-weight: 600;
  }

  .responsive-table td[data-label="#"]::before,
  .responsive-table td[data-label="✓"]::before {
    content: "";
  }
}