When the box-sizing is set to border-box, it can sometimes cut off the "close" button. This issue seems to be more prevalent when using Foundation 3 by Zurb.
The snippet of code that may be causing conflicts with fancybox is as follows:
* {
box-sizing: border-box;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
}
While the author might need to consider border-box in their calculations, I am curious if there is an easy CSS override for this behavior.
This Fiddle demonstrates the problem where you can observe how the close button gets cropped: http://jsfiddle.net/jonthomas/SxZuR/4/
You can also find more information about this issue on github: https://github.com/fancyapps/fancyBox/issues/311