Is it possible to add a custom css file to a fb:like-box? For example, I would like to remove the borders around the iframe. Thanks
The new like-box does not accept the "css" attribute. You have to use the old fb:fan plugin to achieve it.
For example:
<fb:fan profile_id='[PAGE_ID]' width='300' height='256' show_faces='true' stream='false' header='false' css='[CSS_URL]'></fb:fan>
Remember to add the "all.js".