The value italic is the only option you are likely to want to use. You could also try normal or oblique.
In textcss.html delete the heading Things we have done and the list after it. Replace those with this list:
<h2>Some font styles</h2> <ol> <li style="font-style:italic;">italic text</li> <li>bold text</li> <li>normal text</li> <li>sized text</li> </ol>
Save textcss.html and view (obviously only the italic works so far).