<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
</head>
<body>
<div style="position:relative">
<div style="background-color:#ffc815;color:#000;float:left;width:200px;height:40px;">
<div style="padding: 10px 20px">Discover the experience</div></div>
<div id="mask" style="position:absolute;top:0;left:0;width:0px;height:40px;overflow:hidden">
<div style="background-color:#000;color:#ffc815;float:left;width:200px;height:40px;">
<div style="padding: 10px 20px;">Discover the experience</div></div>
</div>
<div id="button" style=position:absolute;top:0;left:0;width:200px;height:40px;"></div>
</div>
<script>
$('#button').mouseenter(function(){
$('#mask').animate({width:200});
}).mouseout(function(){
$('#mask').animate({width:0});
});;
</script>
</body>
</html>