Where do I find the files to edit how my directory displays HTML/CSS

It’s pretty straight forward: I just want to edit the php theme files that output the various directory pages and the accompanying CSS file.

I have tried changing damn near every file in wp-content/plugins/directory/themes/default/ but nothing I do changes the layout in any way. I’ve even deleted the entire folder and the directory still displays exactly the same, so I’m clearly editing files in the wrong area.

I am quickly loosing patience with this plugin. Any assistance would be appropriated.