There will be some custom css classes on the list view so you will also need to find which classes are used on your page / list view and copy these custom styles as well. Once you identify which custom styles are used then you can go to project directory > theme > styles > web > sass and go to relevant folder / sass file and copy them. (If you are copying these custom styles to different project them make sure you compile your sass, you can use Calypso to compile).
Hope this helps!
Use Bootstrap classes that Mendix provides, here is the link to the Medix helper classes
Or else you can do applying your custom CSS using SASS