How do I increase the font size in an iframe?

I have tried set CSS Style to "font-size" "24px or "font-size" "x-large"

Nothing seems to work. While I'm at it, having a hard time changing the font style or type as well.

border-style, border-color, background-color all seem to be working fine.

Thanks.

You can't - the iframe content defines its styles, the parent page can't control it.