I thik I ruined my design with code -please help, bottom borders of some buttons gone in Firefox!

I entered some CSS code (without ever actually saving it) without knowing much about it and now the bottom borders are gone for some of the buttons. They are still there in Safari, but not in Firefox weirdly, where they keep re-appearing and disappearing while scrolling up and down the page (instead of constantly being there). 

I already reseted all the button styles. Is there a way to make them re-appear in Firefox? Any way without using code?

My page is not yet published by the way.

Thank you

I found out that it has nothing to do with any code I entered (I never saved any of it anyway). Instead, it happened because I selected Max. Columns: 2 (previously, it was 3). This is in a slider of my featured posts on the homepage of my blog. If I select Columns: 3, the buttons are not aligned because the headings above them have different lengths (see photo below).

I definitely want to use Max. Columns: 2, not 3. Is there a way to do this without losing the bottom border in Firefox?

Thanks

Can you share link to this page? We can check easier