Your site works on GH Pages as a demo and that is on Jekyll 3
So I suggest adding to the gemspec file. Otherwise anyone who installs the theme will get an error that Jekyll 4 is missing or Jekyll 4 will be installed, when they want Jekyll 3
E.g.
Gemspec file
">= 3.9, < 5"
And Gemfile and lockfile should be
gem "jekyll", "~> 3.9"
Also a note on the README would be nice to say 3.9 and 4 are both supported.
Your site works on GH Pages as a demo and that is on Jekyll 3
So I suggest adding to the gemspec file. Otherwise anyone who installs the theme will get an error that Jekyll 4 is missing or Jekyll 4 will be installed, when they want Jekyll 3
E.g.
Gemspec file
And Gemfile and lockfile should be
Also a note on the README would be nice to say 3.9 and 4 are both supported.