To run the website offline, first you need to install Jekyll. Make sure the versions of the following packages are the same:
For Windows 10:
ruby -v # ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x64-mingw32]
gem -v # 3.1.4
bundle -v # Bundler version 2.1.4
jekyll -v # jekyll 4.1.1
Then you can run the website on your machine using:
bundle install
bundle exec jekyll serve