I followed the tutoriel to create a personalized theme and I meet a problem with the page error. I have no contents for the moment, Antimatter theme show “Error 404 Woops. Looks like this page doesn’t exist.” All is well
I copied the file user/themes/antimatter/templates/error.html.twig in the directory user/themes/mypersonaltheme/templates/error.html.twig. Once the new theme was activated, I have the header which displays but not the contents of the file error.html.twig.
As you can see it extends a partials/base.html.twig file, and then it overrides the content block. If your mypersonaltheme doesn’t define this content block, then nothing will display.
So just make sure you have a content block definition like in Antimatter: