The following needs to be edited:
style.css line 830:
to something like:
I also added some padding so that should help with the look, otherwise your text is right on the border.
I would recommend not editing the main file style.css because if you ever update your theme, all of your changes will be over-ridden (which is no fun, I promise).
Instead you can use a child theme, which will make the changes to your website but not be over-written on updates. Here's some info on a child theme:
I hope that helps.