Character sheet Images Best Practices

I'm setting up for my first charactersheet commit and I'm wanting to figure out if there's a best practices for images used in the charactersheet. At the moment, I have references to imgur but I figured it'd be more stable and beneficial to have the assets in the github, but quality control of this sort of thing seems variable, and of the sheets that do have image directories, their css image references are still using raw URL references instead of relative addresses... so maybe you can't do relative links? I dunno; But it'd be nice to know if I change all my images to things like: background-image: url('./images/metalbar.jpg'); if that'd suddenly break and I'd have to revert back to URL links... 

I think, and I may be wrong, that you can use the relative addresses if the images reside with the CSS file in GitHub otherwise you must use raw URL if placed in a separate folder - which seems to the common practice. I am real new to HTML and CSS and just learned how to place an image in the character sheet I am using so I may be completely wrong.

I think its always best to use the raw addresses for images stored in github. IIRC, the way roll20 accesses the images means the relative addresses are unreliable. The advantage of storing the images on github is not the ability to use relative addresses, but the fact that all the assets for the character sheet are stored in the same place.

I've uploaded my sheet image to github and after it was merged, I took the image's url (right click the github image and select copy url) then placed it in the appropriate line in my sheet. I'm still working on the sheet tweaks so I have not uploaded the latest code to be merged but the github image shows in my sheet.