Take a look below. I added
position absolute
with
left
and
top
. This should get you close to what you want; though you'll probably need to tweak it a bit. Below is an updated test of your sample.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title> New Document </title>
<style>
.centerimage {text-align: center;
position:absolute;
left:50%;
top:50%;
}
</style>
</head>
<body>
<div class="centerimage" style="border: 1px solid #000;">
<img src="https://codeproject.global.ssl.fastly.net/App_Themes/CodeProject/Img/logo250x135.gif" />
<p>you left the group</p>
</div>
</body>
</html>