How do you edit CSS in IE Developer Tools?

I'm using Internet Explorer's Developer tools to try to debug an issue I'm having with a web page.

When I highlight elements the CSS comes up on the right hand side but I don't seem to be able to add new rules or properly edit the existing CSS.

Trying to add a "display:block" property to a class, I tried to edit an existing rule that didn't matter (background-color:transparent) but as soon as I change it the rule disappears!

Am I missing a trick here somewhere?

For a quick addition to test and see the effect I do it a bit differently.

With the HTML tab selected choose the "Attributes" panel next to Style, Trace Styes and Layout.

Click the "+" button and begin typing the css style you would like to add. The new style attribute is added automatically in the DOM view panel.

Hope this helps.