Additional CSS and JS config options do nothing

Hi. I'm new to Voyager and I can't find a way to change the Admin panel's style. The 'additional_css' option in the config file does absolutely nothing, same with 'additional_js'.

I'm considering just altering the code in the vendor folder, as terrible an idea as I know that to be, as I'm at the end of my rope and can't figure out how to change anything otherwise.

What am I doing wrong?