Fill in Form - white background and white font in drop down menu

Site URL: https://www.pushkinhouse.org/virgin-london-marathon-2021

Hi there, 

I have added this form to the page on our website and I'm happy with the background colour (our brand colour) and white font which works well everywhere else on the site https://www.pushkinhouse.org/virgin-london-marathon-2021

however, when you click on the drop down choice you can't see the text, because it's white on the white background. When I changed it to black, the text overlay everywhere else had changed to black too. 

Is there a way of changing the font colour in the drop down only or changing the font colour of the form only?

Thanks in advance!

dropdownfine here. Do you still need help?