ul {
list-style-type: none;
margin: 0;
padding: 0;
overflow: hidden;
background-color: yellow;
}

li {
float: left;
}

li a {
display: block;
color: black;
text-align: center;
padding: 16px;
text-decoration: none;
}

li a:hover {
background-color: blue;
}