Help with wordpress standart gallery CSS!?

Hey!
I’m trying to change the default photo gallery to show up as at this site http://webplantmedia.com/starter-themes/wordpresscanvas/features/gallery/ but I can not change it,found in the CSS code lane that is responsible for displaying the gallery, what exactly commands there need to be placed, to turned out the way I want? Help please!

https://wordpress.org/plugins/gallery/