Icon for button in quick reply toolbar

[fightsol]

Hello.

I have added a spoiler button to the quick reply toolbar.

But i have been trying for days figure out how to show an icon.

Example: http://www.fightsol.com/foros/showth...d-UFC-Vol-III/

If you go to the toolbar of quick reply, the previous icon to the last one (that is code button) has no image.

The image i want to put is called spoiler.png and is located in /images/editor

Any idea on how can i put it. I can't edit the css cause i think the code for the buttons in quick reply toolbar generates automatically.

Thank you.