[Plugin: NextGEN Gallery] Slideshow floating on the left of a text

Hi there,
I would like to have a slideshow on the left hand side of the page, and a text on the right hand side of the page.
I’ve been in the Editor part of the plugin section, trying to modify the .slideshow of the following page : nextgen-gallery/css/nggallery.css
but nothing happens! I’ve been trying to modify the margin, the float, etc… nothing changes on my page, and I can see it’s written (inactive) next to the title of the page “nextgen-gallery/css/nggallery.css” when my plugin is active.
If someone has the answer, I would highly appreciate 😉
Thanks a lot!!

http://wordpress.org/extend/plugins/nextgen-gallery/