Widen Sidebar in Craftiness Child Theme

I know a lot of people have asked about widening their sidebars, but I can’t seem to find any answers that help me! So please excuse asking about this yet again….

I’m on the Craftiness Child theme on Genesis, which is a fairly recent theme (I think), and I can’t find much support on it.

I’d like to widen my sidebar so that it accommodates a 300×250 sidebar ad. I am SUPER new to editing .css in WP, so please use small words and give me baby steps ??

Please and THANK YOU!

this is me: https://www.somethingswanky.com