How to load assets from the static folder in a CSS file?

I think this isn’t really a Hugo issue, it’s more to do with how CSS interprets urls.

According to W3

Partial URLs are interpreted relative to the source of the style sheet, not relative to the document:

So I think if you do

    src: url('./fonts/charter_regular-webfont.eot');

(i.e. starting urls with a dot) then the browswer will load the font files from a relative directory, rather than working a directory based on web root.