Enable user stylesheets

i. Enter about:config in the URL bar.

ii. Search for toolkit.legacyUserProfileCustomizations.stylesheets and set it to true.

Get the configuration files

i. Enter about:support in the URL bar.

ii. Find Profile Directory and copy the path next to the Open Directory button.

iii. Go to that directory:

cd path/to/profile/directory

iv. Clone the repository into a new directory named chrome:

git clone https://github.com/sejjy/zenplified.git chrome

Restart Zen Browser to apply the changes.