<!doctype html>
<html>
<head>
<title>Center alignment</title>
<style>
.box-center {
margin: auto;
width: 50%;
border: 3px solid green;
padding: 10px;
text-align: center;
}
.img-center {
display: block;
margin: auto;
}
</style>
</head>
<body>
<h2>Center alignment</h2>
<div class="box-center">
Hello World
</div>
<p></p>
<img class="img-center" src="http://via.placeholder.com/200x100">
</body>
</html>