Hi !
I need your help to have a blank CSS of SuiteCRM to personnalized my colors, i need to custom for my employes. I think when the CSS was end i just need to use the module loader to install my new theme it’s true ?
Thank’s for your help 
This article is a bit outdated, but you can get a sense of what is involved:
https://pgorod.github.io/Customize-SubTheme/
You need to know about SASS generation, and about the sub-theme concept (starting in 7.10.0).
The thing that is missing from that article is a correct explanation of how to achieve the same thing in an upgrade-safe manner, respecting the “custom directory” mechanism, which you can read about here
https://pgorod.github.io/Custom-folder/
I’m not sure if you could achieve this through Module Loader, I doubt it…