Is there a way to overwrite Control Panel css?

I’ve made some tweaks to the control panel css, but I’ve had to do it in the ‘core’ file: themes/ee/cp/css/common.min.css

I’ve tried to duplicate under: themes/user/cp/css/common.min.css

but no luck, any pointers?

I’d like to be able to do this without creating a plugin if possible

thanks