In your theme “minimalistic” you will find a file named “menusm.css”, I think it’s colliding with the code of “sf-grey.css” of your plugin. May be in your “style.css”, the “menusm.css” is imported like: @import url('menusm.css');
Try commenting it out with /* & */ like: /*@import url('menusm.css');*/
So that it won’t load. Then try refreshing your site, and let’s know it works or not.
But I’d like to remind you that, it’ll cause some other problems too. Because it has some other css codes, necessary for your site design too.
So, it’d be better, if you not comment out the whole file but some of the colliding codes only. You can use FireBug in Firefox to get all the colliding codes, and then can comment ’em out specifically.