Short answer: no.
There is no way to do what you want with CSS included in your page because CSS only applies inside document boundaries.
And you can't circumvent this with JavaScript either, by dynamically inserting stylesheets inside the object's (/iframe) content, due to the same origin security policy, which prevents you from affecting the content of an embedded document that is on a different domain as your container page.
The kind of vulnerabilities that this security policy prevents are called cross-site scripting vulnerabilities.
