Adjusting the size and position of the "Share this" and "Like this" sections

I have the Jetpack plugin installed and the “Share this” and “Like this” features enabled. Right now, by default, they appear stacked on top of each other and with larger font sizes than I would like. I’d like to make the size of the headings (i.e., “Share this” and “Like this”) smaller and have them stacked next to each other, instead of sitting on top of each other as they do right now. Mostly I’m trying to make it so there’s not so much space between the end of a post and the “Leave a Reply” section.

To see what I mean, feel free to check out a post on my blog (assuming I haven’t figured out a way to change it by the time you’re reading this): http://mchilliard.tk/blog/2014/10/27/adventures-in-not-getting-arrested/ (I know everything is pretty plain right now. I’m still working on the design.)

I couldn’t find anything for it in the Nirvana Settings, or elsewhere, so I’m assuming I’ll have to add custom CSS (via the Nirvana Settings) or edit the CSS–which, I noticed, gets overwritten any time the theme is updated, so that’s not really an ideal option. Any help would be appreciated!