Does customCSS.css get overwritten during updates?

I’m looking at customizing a few things on my Self-Hosted install.
If I make changes to customCSS.css, will those get overwritten during an update?

If so, is there a better way to make css changes that will remain after updating?


You can set custom CSS for the portal in the settings, any other changes would be overwritten.

Is that just for the Client Portal? Is there a way to do the same with the Admin Site?