See this custom.css file. It is example of how to simplify the look of administration template.
https://github.com/PhocaCz/CustomCSS
Just download custom.css and upload it to CSS folder of administration template, for example to:
administrator/templates/isis/css/
Custom.css is automatically loaded in administration
I do not know if there's something missing. But if you are interested, then just extend it or create new own variant of it.

