The epub standard doesn't say what version of CSS must be supported. There were no guarantees modern CSS would work so I wouldn't call the renderer broken.
> illegal values, or values with illegal parts, are treated as if the declaration weren't there at all
So a conforming implementation would ignore that max-width property declaration, not raise an error.
And those earlier versions of ePub which defined a required subset of given CSS standards? The forwards-compatible parsing rules were part of their subset.
Ignore != Fatal error
As such, whenever I get my hands on an .epub file, I go to an online converter, convert it to a .pdf file and nuke it from my system. Then the .pdf gets opened in my FoxIt.
It‘s working great on Windows, as well.
Now doing that with PDF would actually make it challenging.
Annotation system (with pics): https://wiki.kavitareader.com/guides/readers/epub/#annotatio...
It's getting very tiresome.
It looks like not a whole lot has changed in that space -- the readers are still the gate for what you can do with the format. Who's available to make a CanIUse for epub readers, to shame them into compliance? (only partly /s)