Defining the body style like this:

body {
width: 800px;
margin-top: 25px;
margin-left: 25px;
background:#0000FF;
color:#FFFFFF;
font-family:Verdana, Arial, Helvetica, sans-serif;
}

Then create a Div with class .wrapper and put it immediately after the body and before the end body tags with this style:

.wrapper {
background-color: #0099CC;
padding: 2em;
border: thick ridge #FFFF00;
}

Note the border color is yellow just to show the differences.

I could have used em (elements) in the body if I wanted.

 

This will make a good "boxed" web page.