position problems with zoom in / zoom out resolution screen

Hi, my problem, and i think is a great problem, is that with zoom in / zoom out (ctrl +, ctrl -) i can’t give the slider a fixed position, so it goes left and right.

I’ve tried to modify in the CSS the properties about the slider position but nothing happens.

How to fix?

Thanks,

Alex

http://wordpress.org/extend/plugins/wp-nivo-slider/