JSFiddle - React, Tailwind, and code Playground
HTML
<div id="1">ID with digit</div>
<div class="1">Class with digit</div>
<div id="one">ID with word "one"</div>
<div class="one">Class with word "one"</div>CSS
#1 { background: red; }
.1 { background: red; }
#one { background: red; }
.one { background: blue; }