Form block, change dropdown arrow color

Is there anyone who has a css code for changing the color of the dropdown arrow of a form block? 

I've managed to change the color of all form field details, but for some reason the dropdown arrow is still black (I want it to be green). 

This is the site:

https://yellow-cube-g76x.squarespace.com/shop

Password: Trio

Thanks in advance!

Hi LiveM, 

Have you ever figured this out? Running into the exact same problem. 

Thanks in advance. 

@TimoBluntt I hadn't figured it out no, but your code works perfectly! Thanks!