Publishers styling is a Device feature. It means use the CSS
Some devices that is All or Not-a-thing used switch. Some allow some CSS control on top of the devices.
Calibre's viewer allows your choice for DEFAULT generic font classes (image) lik serif... That are used if any other font called is unavailable. eg
font-family: "Rickety Old Typewriter", monospaced;
As you may have observed, many
cleaning tools fail once a document has become
corrupted by a partial removal of intertwined elements.