fade

HTML

<a class="tab">Home</a>

CSS

a.tab {
    background-color: #f4f4f4; 
    font-family: arial;
    font-weight: bold;
    font-size : 40px;
}

a.tab:hover {
   background-color:#d4d4d4;
    
     -webkit-transition: background 300ms ease-in 200ms;
    -moz-transition: background 300ms ease-in 200ms;
    -o-transition: background 300ms ease-in 200ms;
    transition: background 300ms ease-in 200ms;
}