https://github.com/b4n/geany/commits/vte-2.91 seems to work, but for background images. I can't seem to find a non-crazy way of implementing it (I can't get CSS to do it), and I don't care enough about it to implement a crazy way. But we still need a proper thing here, either implementing it somehow, or dropping the feature altogether (I'd vote for the second, but well).