:root {
  /* Colors */
  --bg: #f4f6f8;
  --text: #1a1a1a;
  --primary: #2c3e50;
  --accent: #3498db;
  --card-bg: #ffffff;
  --secondary-text: #444; /* Added for the p tag in header */
  --border-color: #ddd; /* Added for border */

  /* Spacing - common rem values */
  --spacing-xxs: 0.25rem; /* 4px */
  --spacing-xs: 0.5rem;   /* 8px */
  --spacing-sm: 1rem;    /* 16px */
  --spacing-md: 1.5rem;  /* 24px */
  --spacing-lg: 2rem;    /* 32px */

  /* Font Sizes */
  --font-size-base: 1rem; /* Equivalent to 16px if html font-size is 16px */
  --font-size-sm: 0.95rem; /* Equivalent to 15.2px */
  --font-size-lg: 1.5rem; /* Equivalent to 24px */

  /* Component specific dimensions */
  --sidebar-width: 13.75rem; /* 220px / 16 = 13.75rem */
  --card-min-width: 15rem;   /* 240px / 16 = 15rem */
  --card-max-width: 18.75rem; /* 300px / 16 = 18.75rem */
  --card-border-radius: 0.625rem; /* 10px / 16 = 0.625rem */

  /* Shadows */
  --box-shadow-sm: 0 0.25rem 0.625rem rgba(0,0,0,0.05); /* 0 4px 10px */

  /* Breakpoints */
  --breakpoint-md: 48rem; /* 768px / 16 = 48rem */
}

/* Base HTML font-size for rem calculations */
html {
  font-size: 16px; /* You can adjust this base if needed */
}

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

body {
  font-family: 'Segoe UI', sans-serif;
  background-color: var(--bg);
  color: var(--text);
  line-height: 1.5;
  font-size: var(--font-size-base); /* Ensure body also uses rem for its base font */
}

.back-button {
  display: inline-block;
  margin: var(--spacing-sm);
  padding: var(--spacing-xs) var(--spacing-sm);
  background: var(--accent);
  color: #fff;
  text-decoration: none;
  border-radius: var(--card-border-radius); /* Using card radius for consistency */
}

.challenge-header {
  padding: var(--spacing-sm) var(--spacing-lg);
}

.challenge-header h1 {
  font-size: var(--font-size-lg);
  margin-bottom: var(--spacing-xs);
}

.challenge-header p {
  font-size: var(--font-size-sm);
  color: var(--secondary-text);
}

.dashboard {
  display: grid;
  grid-template-columns: var(--sidebar-width) 1fr;
  height: 100vh;
}

.sidebar {
  background-color: var(--primary);
  color: white;
  padding: var(--spacing-lg) var(--spacing-sm); /* Adjusted padding to use variables */
  position: relative;
  z-index: 2;
}

.main-area {
  display: flex;
  flex-direction: column;
}

.header {
  background: var(--card-bg);
  padding: var(--spacing-sm) var(--spacing-lg);
  border-bottom: 0.0625rem solid var(--border-color); /* 1px / 16 = 0.0625rem */
  z-index: 1;
  position: sticky;
  top: 0;
}

.main-content {
  padding: var(--spacing-md) var(--spacing-lg);
  overflow-y: auto;
}

.cards {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-md);
}

.card {
  background: var(--card-bg);
  border-radius: var(--card-border-radius);
  box-shadow: var(--box-shadow-sm);
  padding: var(--spacing-md);
  flex: 1 1 calc(50% - var(--spacing-md)); /* Uses the variable for gap */
  min-width: var(--card-min-width);
  max-width: var(--card-max-width);
}

/* Responsive for smaller screens */
@media (max-width: var(--breakpoint-md)) {
  .dashboard {
    grid-template-columns: 1fr;
  }

  .sidebar {
    grid-row: 1;
    text-align: center;
  }

  .cards {
    flex-direction: column;
    align-items: center;
  }

  .card {
    width: 100%;
    max-width: 90%; /* Percentage units are fine as they are responsive by nature */
  }
}