Editing Form Fields CSS

I want to have first 2 rows (dropdown + VAT) in 1 row but with even after I added a CSS class attribute in form setting to both of them I couldn’t make it work: https://prnt.sc/10v7y80
If I use rmrow I would edit the other fields too.

The page I need help with: [log in to see the link]