Iframe cross domain html page with dropdown menue expanding issue

Iframe cross domain html page with dropdown menue expanding issue

I have a aspx page which loads a third party's header.html page (which I
have no control of). I have a fix height on the iframe. for example:
iframe
style="width:1024px;height:180px;margin-left:auto;margin-right:auto;"
frameborder ="0" scrolling ="no" src
="https://somethirdparty.site.com/pagepart/header.html"
The problem is on the third party's header.html page there are some css
menu items with drop down sub-menu links (appears when mouse hovers). The
submenu gets cutoff --not expanding entirely. I tried to change the iframe
height to 100% or auto, it gets even worse--that bottom of the header.html
gets cutoff.
My question is what is the best way to handle this situation. Is there a
way to expand and overlay the dropdown submenu items to my main page?
Thanks in advance.