Width of Dropdown field doesn’t work.

Hey Guys! First of all thanks for the great plugin.
I’m trying to edit the width of the Dropdown fields on one Page. To ad a border and change their color worked without any problem, change the font size works too but the width doesn’t seem to work. I need a max-width of 59px for the dropdown fields. Do you have any advice for me, how I can solve this problem?

Thanks in advance

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