There's a closed pull request on the void-packages repository

greybird-themes: update to 3.23.3, remove gtk-engine-murrine dep, adopt.
https://github.com/void-linux/void-packages/pull/50285

Description:
removes dependancy on gtk-engine-murrine. I don't see why a bunch of themes need this dependency. It is only needed for gtk2 support, so if users really need gtk2 support, they could just install that it manually. I don't think it makes sense to pull in gtk2 when installing a theme package.

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