Is a selector like
.a, .b, .c, .d, .e, .f, .g, .h, ......... , .zzzzz {font-size:16px}
bad for performance? If yes how and if no why?
I Googled and read a lot of posts including the ones by Mozilla and couldn’t find any mention of having a large number of class names as a selector being bad.
No, there is no performance problem here.
What is bad is a long selector involving many checks but your selector is in fact a sequence of selectors, equivalent to
Selectors with just a class are among the most efficient ones.
There’s no real problem, even if you probably should have less classes in order to manage your code more easily.