html {
  font-family: Arial, Helvetica, sans-serif;
  background-color: black;
  color: lightgrey;
}
h1, h2, h3, em, i, b {
  color: white;
}
body {
  margin: auto;
  max-width: 30em;
  padding: 1em;
}
h1, h2, .center {
  text-align: center;
}
a {
  color: lightblue;
}
a:hover {
  color: yellow;
  background-color: darkblue;
}
a:active {
  color: black;
  background-color: lightblue;
}
dt {
  padding: 0.5em;
}
.hover:hover .show {
  display: none;
}
.hover .hide {
  display: none;
}
.hover:hover .hide {
  display: inline;
}