Why is this simple html and css code not showing anything?

Programmer Question

html:

css:

body {
margin:0;
padding:0;
}

#wrap {
width:750px;
margin-right:auto;
margin-left:auto;
background:#008B00;
}

The html file is called qa.html, and the css file is called qa.css
The two files are in the same directory.

Find the answer here