Differentiating staging and production admin pages by colour in Magento 2

I often have the admin pages for my staging sites and my production site open simultaneously. There's a big risk I'll inadvertently take an action on the wrong site so I manually edit the admin css files for each to make the toolbar a different colour in each. That way I can see instantly which site I'm on.

I was wondering whether there's a way of injecting a class (or something similar) from the htaccess file for each site. This is something fixed for each site so wouldn't need me to edit the css file each time I make a change that affects it.