Snow License Manager has a CSS file called custom.css in content/styles/, similar to that which is in the Snow Automation Platform. When SAP 3.7.0 was released, one of the enhancements was removing the custom.css from the SUS package to prevent custom work being overwritten every time you do an update
Theme files (custom.css and customResponsive.css) have been removed from the SUS package. This removal ensures that user-created styles will no longer be overwritten when updating.
Is there a reason why this hasn't been done for SLM 8 or SLM 9? It's a bit annoying having to update the custom.css file every time you update because the SUS wipes it.