Use of Animation-Direction Property

<style> 
div 
{
    width:250px;
    height:400px;
    background:skyblue;
    position:relative;
    -webkit-animation: myfirst 5s infinite; /* Works only on Safari and Chrome */
    -webkit-animation-direction: alternate; /* Works only on Safari and Chrome */
    animation: myfirst 5s infinite;
    animation-direction: alternate;
}

/* Safari and Chrome */
@-webkit-keyframes myfirst 
{
    0%   {background:red; left:0px; top:0px;}
    25%  {background:yellow; left:200px; top:0px;}
    50%  {background:blue; left:200px; top:200px;}
    75%  {background:green; left:0px; top:200px;}
    100% {background:red; left:0px; top:0px;}
}

@keyframes myfirst 
{
    0%   {background:red; left:0px; top:0px;}
    25%  {background:yellow; left:200px; top:0px;}
    50%  {background:blue; left:200px; top:200px;}
    75%  {background:green; left:0px; top:200px;}
    100% {background:red; left:0px; top:0px;}
}
</style>