To contribute to the docs, fork the composer/composer repository and add or change a file in the doc directory. Documentation sources can be browsed at https://github.com/composer/composer/tree/main/doc
Documentation is then automatically generated on getcomposer.org
To change JS and CSS, make sure you run npm install first and then use
npm run dev or npm run build to build new assets from the sources.
The output of build should be committed to be deployed, but please do not commit it if you are sending a pull request.