JSFiddle - React, Tailwind, and code Playground

HTML

<a class="amplink" id="video">amplink</a>
<a class="somethingelse">not amplink</a>

JavaScript

var all = document.getElementsByTagName('a');
for (var i = 0, o; (o = all[i]) != null; i++) {
    if (o.className == "amplink") {
         o.style.backgroundColor = "lime";
    }
}