Actually I was also beaten by this.
It seems that for any
rgba value e.g.
rgba(000, 000, 000, 0.7); and also if a color value is set to
transparent @tdewolff 's minifier outputs invalid hexadecimal numbers that fail W3C validation.
I have amended the title of this thread because this is a bug.
However I am busy as hell (and will be from now on) I certainly do not have the time to make test repos,
open a bug upstream etc. Time is scarce for me.
Filed bug report upstream myself. Feel free to participate:
I closed the above issue because I had a look at the minifier’s Docs and there is already a flag that addresses the invalid CSS output.
So I opened the following issue in Hugo’s main issue tracker: