How to Modify Casiopeia Template Joomla 4

 Cassiopeia template is built using a mix of PHP, XML, Javascript and CSS files (occupying, in total 1½MB). The main template file used by Cassiopeia (..//media/templates/site/cassiopeia/css/template.css)—which you should never edit—is over 300KB containing 1,600 rules. So, if you want a "comprehensive list" of all the rules, you can find them in that file.

The problem with producing a single document that lists all of the CSS descriptors and what they do is that it would be document several hundred pages long, that would be subject to change with new releases of J!, that would be out-of-date in a very short time and something that no-one would read. For people who understand CSS, the language is self-documenting.

As @Per mentions, the method used by people who want to customise the styling of HTML elements (e.g. "button" colours) is to use the inspector (or developer) tools built into the web browser. That's how we do things. We don't refer "documentation".

There is, however, a useful guide that was published in the Joomla Community Magazine in February last year: Joomla 4 – Cassiopeia Template – a bunch of Tips & Tricks. It's a matter of opinion whether that article could be characterised as being adequate for most purposes.

Sometimes people do have difficulties with CSS. I consider myself fairly fluent with CSS but we all learn something every day. :laugh: While it's not our job to provide a free, surrogate website development service—this forum is a self-help resource where we point people in the right direction (we hope) where they can find the answers to their questions—if you're stuck and have a specific question then please start a discussion topic about that matter and we'll do what we can. I hope this general answer to your general question helps.