ul {
    list-style-type: none;
    margin: 0;
    padding: 0;  
    background-color:black ;
    position:fixed;
}
li {
    background: green;
    position:relative;
    font-family: Calibri;
    font-size: 20px;
}
li a {
    display: inline-block; /*Per poder tenir alçada*/
    color: black;
    text-align: center;
    padding: 4px 6px;
    text-decoration: none;
}
li a:hover{
  background-color: white;
  color: black;
}