Is there a way to replace the generated '"x" icon for the close function on lightbox?

Right now the "x" that appears is too thick and is contained in a circle and i'd like to just have an "x" in a thinner slab sans serif font without any circle.

I'm not sure this is possible, since the button is generated by internal JavaScript. 

It might be possible to create a lightbox using the Source code but, it will require some JavaScript to do so.