JSFiddle - React, Tailwind, and code Playground
HTML
<div class="class1">has one</div>
<div class="class2">has another</div>
<div class="class1 class2">has both</div>
<div class="class3">has anything else</div>CSS
div.class1.class2 { background: red; }
div:not(.class1):not(.class2) { background: grey; }