Shipping bar goes out of alignment when scrolling.

My site at Bickettandboone.com is using your plugin. It works when at the top of the page, but when I scroll it goes out of alignment, making it not usable on mobile. I thought maybe it was something I could edit in the CSS but I don’t see anything there. I thought maybe it was because I was using a sticky header, but I turned that off and it still did it. I appreciate any help.