How to customize looks/style of member directory

Hi! I’d like to change the looks of the member directory filters. Specifically, I want to move the filter boxes to the left of the page in its own box. I haven’t been able to do this through CSS as I understand that the filters and member profiles are in the same div and reducing the margin only moves the entire content (filter + member profiles).

How can I edit only the appearance of the filters? I’m happy to look into the files as well, I just couldn’t find the appropriate php file so far.

Thank you for your help!