No limitation, -so long as no declaration/selector over-rules another, previously-stated. Then, order-of-precidence takes 'hold and the last-stated is the obeyed.
<h1 class="first second third">HEADER TEXT</h2>
would be GREEN text, because the class "third" is stated last in the precedence order in the HTML..
It gets complicated when you want some styles from class="first" and class="second" if you need "display:block;" and the second class states "display:inline;", and so forth...
Myself, if more than TWO classes are needed, I combine the stated-needed Declarations and create another new class (like, class="four") and use solely that, instead of combining three potentially-conflicting classes.