COmanage and CILogon support custom themes via their own individual CSS files.
CILogon.org uses CSS Bootstrap 4.x (https://getbootstrap.com/docs/4.6/) under the hood. The CSS for CILogon “skins” is stored in the database and output to a <style> block in the <head> of the HTML.
Some examples include:
https://cilogon.org/?skin=access
https://cilogon.org/?skin=biocommons
https://cilogon.org/?skin=illinois
https://cilogon.org/?skin=lsst
https://cilogon.org/?skin=ncsa
When creating CSS, make sure it also works with https://cilogon.org/me/ as there are HTML elements on that page not shown on https://cilogon.org/.
Share the CSS with the CILogon team via a GitHub repo or a drive sharing link, like Box.com, oneDrive or Google Drive.