html {
  color-scheme: light dark;
}

body {
  width: 35em;
  margin: 0 auto;
  font-family: Tahoma, Verdana, Arial, sans-serif;
}

.btn {
  display: inline-block;
  padding: 10px 20px;
  background-color: blue;
  color: white;
  text-decoration: none;
  border-radius: 4px;
  font-weight: bold;
}

.btn:hover {
  background-color: darkblue;
}