The same applies to any class used in Joplin. That's why the warning in Joplin states. "... styles you define may break from one version to the next. If you want to use them, please know that it might require regular development work from you to keep them working..."
I believe that @tessus has already been asking, either somewhere on this forum or on GitHub, that this is considered for a future release . He has also created a wiki list of css elements which should have a class and a wiki list of useful customisations.