Cant access css for a sidebar widget

Apologies in advance if this is a problem that has already been addressed in a forum but if it has I can’t find it. I’m sure it is a simple fix, but having only basic knowledge of php/css i could use some expert advice.

In my sidebar on my site I have an external Iframewhich is a booking system. As far as my knowledge goes, other than rudimentary size changes etc I shouldn’t be able to change much of this, and usually i would just let it go. However I have, in the dim and distant past, obviously been able to change the colour of it, it used to be grey and I changed it to the purple colour. Im assuming through css. This has been annoying me to the point ive registered here. Im by no means an expert at html, php or css, but i can manipulate it, which ive obviously done before and totally forgotten. My site is hosted elsewhere so i dont have access to wp-content.php,and when i try to find where to sort it through firebug etc im lead to an iframe.php which is obviously with my host as i cant access that. Normally I would at this point just say well this is what happens when someone else hosts your site, however since I have in the past been able to change the background colour of the booking system I should be able to change other things but I can’t even find where i did that. If you take a look you will see that the letters are slightly cut off. This isn’t a major prob but it just looks aesthetically wrong. And its annoying:)
my site is: http://www.aberfordhotel.co.uk