JSFiddle - React, Tailwind, and code Playground

HTML

<div class="names">Trevor</div>
<div class="names">Phil</div>
<div class="names">Russell</div>
<div class="names">Charlie</div>
<div class="names">Taylor</div>
<div class="names">Clare</div>
<div class="names">Sophie</div>
<div class="names">Ellie</div>
<div class="names">Jean</div>
<div class="names">Sarah</div>
<div id="selected"></div>

CSS

.names {
    background-color: black;
    width: 150px;
    text-align: center;
    margin: 5px;
    padding: 5x;
    font-size: xx-large;
    color: white;
    opacity: 1;
}

JavaScript

var z = document.getElementById("selected");

var r = function () {
    b = document.getElementsByClassName("names");
    c = [];
    d = [];

    for (i = 0; i < b.length; i++) {
        if (window.getComputedStyle(b[i]).opacity == 1) {
            c.push(b[i]);
        }
    }

    for (i = 0; i < 5; i++) {
        num = Math.floor(Math.random() * c.length);
        d.push(c[num]);
        c.splice(num, 1);
        z.innerHTML += c.length;
        console.log(c.length)

    }

    for (i = 0; i < d.length; i++) {
        d[i].style.backgroundColor = "red";
    }

};

r();