To customise the button with CSS you can't use the usual pseudo-classes of :hover or :active you have to use the zeroclipboard sub-classes: .zeroclipboard-is-hover and .zeroclipboard-is-active . This is because you have the clear Flash element over the top which is blocking direct access to the underlying button.
d_clip_button.zeroclipboard-is-hover { background-color:#eee; }
d_clip_button.zeroclipboard-is-active { background-color:#aaa; }
See the zeroclipboard documentation in more detail under CSS Effects at https://github.com/zeroclipboard/zeroclipboard/blob/master/docs/instructions.md
As to your error in the console check out this answer Uncaught Error: Error calling method on NPObject