How to Customise CSS in Web Panel

I have found the file custom.css in /usr/local/cwpsrv/htdocs/admin/design/css/ and when I use vi to edit the file, right at the top, I am invited to:

/* ------------------Put your custom code here--------------------*/

Except I can't save the file as it is read only.

All I want to do is reduce the size of the orange font in the 'Spark Stats' area.

Are we really not allowed to change the look of CWP or is this an oversight by the development team ?

Is there a 'fix' or 'workaround' ?

you can modify it but every update will replace it and updates are almost every day.
Soon there will be a new version where templates will be available.

you can modify it but every update will replace it and updates are almost every day.
Soon there will be a new version where templates will be available.

Any updates on this?
custom.css should be easily excluded from update.

Additional question: Is there any way to customize the sidebar - except css?
I don't need some buttons like "Billing" so it would be nicer to have a smaller sidebar..

Love to know if we've gotten anywhere with this.  Switching between servers and seeing the same control panel "theme" is just a recipe for mistakes late in the day.  Would be nice if there was a permanent "include custom.css" that survives upgrades.