I just learned that
background-image: url("data:image/svg+xml,%3Csvg ...")
apparently does not work.
I do understand that usage of url() is limited to well known http domains, like the own site and Commons.
I guess data:image/svg+xml is considered to be dangerous, since an SVG document may contain references to really external URL (embedded beacon PNG etc.).
However, could SVG data be decoded by CSS Sanitizer and source inspected whether containing undesired syntax, or free of any harmful components and get released as sanitized-css?