When modifying css files and placing them under the filestore folder, are not taken into consideration. Path: %USM_HOME%\filestore\custom\explorer\scripts\catalogux\resources\css
This behavior has been reproduced with app.css and select.css files.
Release : 17.2
Component : Catalog - Customizations
By design. Expected behavior.
The .css files are not to be designed to be customized, because the CSS files will not go through the standard customization root of file loading.