So what I was already doing (as seen in the first example). It wasn't working because Calibre uses QT-specific CSS property for indentation
-qt-list-indent.
Thanks to this link @kovidgoyal had shared in an older post showing all supported HTML Tags & Attributes and CSS Properties & Selectors:
https://doc.qt.io/qt-5/richtext-html-subset.html
That clears things up. I will have to find some other way to sort my issues.
Thank you!
Edit to clarify: The CSS property
user-select isn't supported.