Color Tester in HTML , CSS , JS

<html>
<head>
<title>Color Tester</title>
<script>
function change(){
HexColor=document.getElementById("a1").value;
document.body.style.background=HexColor;}
</script>
<style>
#ss{border:2px solid #000000;
position:absolute;
top:25%;
left:25%;
margin:auto;
text-align:center;
background-color:#BBBBBB;}
</style>
</head>
<body>
<br/><br/><br/>
<div id="ss"><br/>
<input type="text" placeholder="For Example:- #F5AC42" value="" id="a1"/><br/><br/>
<button onclick="change()">Click To Change Color</button><br/><br/>
</div>
</body>
</html>