<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
#wrapper {
width: 100%;
height: 400px;
border: 2px solid #000;
}
button {
height: 20px;
position: relative;
margin: -20px -50px;
width: 100px;
top: 50%;
left: 50%;
}
</style>
</head>
<body>
<div id="wrapper">
<button type="button">W3Docs</button>
</div>
</body>
</html>