:root {
  --bg-color: #ffffff;
  --text-color: #111111;
  --link-color: #003366;
  --header-bg: #f8f8f8;
}

[data-theme="dark"] {
  --bg-color: #121212;
  --text-color: #e0e0e0;
  --link-color: #66aaff;
  --header-bg: #1f1f1f;
}

body {
  background-color: var(--bg-color);
  color: var(--text-color);
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

header {
  background-color: var(--header-bg);
  padding: 1rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

nav a {
  margin-right: 1rem;
  text-decoration: none;
  color: var(--link-color);
}

section {
  padding: 2rem;
}

footer {
  background-color: var(--header-bg);
  text-align: center;
  padding: 1rem;
  font-size: 0.9rem;
}

button#theme-toggle {
  padding: 0.5rem 1rem;
  background-color: var(--link-color);
  color: #fff;
  border: none;
  border-radius: 5px;
  cursor: pointer;
}