When i said "reenter the HTML Editor", i meant with HTML Editor you are able to go back to the wizard and make changes to the Editor. to do that:
1. in Dreamweaver open the Properties window (Window -> Properties)
2. In Dreamweaver Design View, click on the HTMLEditor
3. in the Property window you should see an edit button, click the edit button and that should launch the HTML Editor wizard.
once the html editor wizard is open click the customize button and then the style tab and then select the css file you want to use in the editor.