html,
body {
  position: relative;
  width: 100%;
  height: 100%;
}

a {
  color: rgb(0, 100, 200);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

a:visited {
  color: rgb(0, 80, 160);
}

button:disabled {
  opacity: 50%;
}