Use an unique scrollbars

If you want to use a height of 100% than you need to remove stuff like empty <p>
or
< ?php /** * Template Name: Racingcards */ ?>

because than 100% is simply not left.

I recommend only to use 99% (because otherwise you would also have to remove any margings or paddings!) and remove the extra elements.

Best, Michael

Ok, with 97% I have one scrollbar, but the problem is this margin:

View post on imgur.com

Please see here:
https://stackoverflow.com/questions/5272519/how-do-you-give-iframe-100-height

you have also to set the html and body to 100% (and remove the not needed elements).

You can set any of the given solutions at the advanced iframe.