This is the stderr looks like

prince: -:style:2: warning: unknown property 'color-scheme'\nprince: -:style:2: warning: unknown property 'supported-color-schemes'\nprince: -:style:2: warning: unknown property 'behavior'\nprince: -:style:161: warning: unknown media feature 'prefers-color-scheme'\nprince: -:style:62: warning: unknown media feature 'prefers-color-scheme'\n\n*** Mercury runtime: caught strange segmentation violation ***\nPC at signal: 139740655820761 (7f17e8269fd9)\nThis may have been caused by a stack overflow, due to unbounded recursion.\n

Would you be able to attach or email me (mikeday@yeslogic.com) the HTML + CSS that causes the problem? It's unlikely to be related to the color-scheme property, that's just a warning about a property that Prince currently doesn't support.

This issue related to a potential crash at program exit if background threads make HTTPS requests using OpenSSL, and has been fixed in the latest build, thanks for letting us know!

This fix has now been backported to Prince 15.4.