Fork Repo

Fork the repository
git clone https://github.com/${yourUsername}/docsify-darkly-theme
cd docsify-darkly-theme
Make changes in CSS Filedocs/css/darkly.css and preview it. later do the same changes in css/darkly.css and css/darkly.min.css folder of root dir and Create Pull Request

Sending Pull Request

Create a branch in your forked repository with a relevant name (e.g enhanced-styling)
Push your changes to the branch
Create a pull request from your branch to master of my branch.