body {
  margin: 0;
  overflow: hidden;
  background: black;
  color: #0F0;
  font-family: monospace;
}

#menu {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
}

#menu a {
  display: block;
  font-size: 2em;
  margin: 20px;
  padding: 10px 20px;
  border: 2px solid #0F0;
  color: #0F0;
  text-decoration: none;
  transition: 0.3s;
}

#menu a:hover {
  background: #0F0;
  color: black;
}