.menu {
  list-style: none;
  margin: auto;
  padding: none;
  width: 600px;
  display: flex;
  justify-content: space-around;
  
}

.menu li {
  border: 1px solid black;
  width: 100px;
  text-align: center;
  display: inline;
}

  a: hover {
  color: green;
  background-color: lightgray;
}