How to change font size when you *don't* control the HTML?

How do you increase/decrease the font size in a web page when you don't control the HTML, but only the div or the iFrame in which the HTML appears?

We have a site that includes user-generated content. This content is essentially uncontrolled, and the HTML can be complex. (It's an "upload your own ebook" app).

We wrap the content for each chapter in a div. We'd like to add a control to the page that will allow the reader to increase the size of the fonts within the div.

A similar question was asked here: Allow users to change font size in a webpage, but the answers won't work because I can't prevent users from adding HTML that specifies font sizes in pixels.

My best thought is to roll through all the text using jQuery an开发者_如何学God adjust, but this is likely to generate problems when font sizes are inherited, because the font in a child element would get adjusted twice.

Is there any generalized solution for this problem?

You can use JavaScript to:

• change CSS attributes
• remove tags from text

I would look into stripping the font size when the book is uploaded.
Alternatively: Tell your writers that their books might not look the right way in everyone's browsers if they specify exact fonts.