A flavor might decide that they want to make modifications to the CSS for the file listings on cdimage.ubuntu.com to be tailored towards their design goals. Originally, Kubuntu was the only Ubuntu flavor to make such modifications, but Lubuntu worked towards making a process that other flavors can easily follow, which is outlined below.
First, you need to have a working copy of the existing CSS and make modifications to fit your needs. This part is dependent on a flavor's artwork team, but the process, in short, is to:
Either using Inspect Element in a browser or by downloading the HTML file for your flavor (so for Ubuntu MATE, for example, it would be this), modify the line in the HTML which includes the CSS to the path of your forked CSS file.
- Wash, rise, and repeat, until you have a CSS file which you believe makes all of the modifications necessary to be consistent with your branding.
Once you have the candidate CSS file, commit it to a Git repository (along with a license and screenshots, if you wish), and push it to Launchpad (this is so permissions are clear, although you can mirror it elsewhere). Then, ask a member of the Ubuntu CD Image Team who works at Canonical (and thus has SSH access) to clone your Git repository to http://cdimage.ubuntu.com/include/FLAVOR-NAME (so e.g. http://cdimage.ubuntu.com/include/lubuntu ).
You then need to ensure that this CSS change is reflected in lp:ubuntu-cdimage. So, add a line to lib/cdimage/tests/test_tree.py (under the test_cssincludes function), lib/cdimage/tree.py (under the cssincludes function), and if you have header changes (which include a pointer to a different website than Ubuntu's and a favicon, which is recommended) you need to modify make_web_indices in lib/cdimage/tree.py to reflect those changes. Once that's merged, do a test ISO build (or wait until the next one scheduled by cron) to make sure your CSS changes have been fully reflected.
Now, all of your pages utilize that one CSS file, and all of those pages can be updated on one push to that Git repository. If you want your pushed changes to be deployed to prod, you don't need to go through the process of requesting merge proposals again, you just need to push your changes and then ask a member of the CD Image Team to do a git pull on that repository.