JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <p>hi</p>
</div>

CSS

.main{
    width: 1000px;
    height: 1000px;
    display: block;
    opacity: 1;
    background-color: green;
    border: 1px solid black;
}

.flash{
    opacity: 0;
}

JavaScript

var flash = true;
var alert = setInterval(function(){
    if (flash) 
       $('.main').addClass("flash");
    else 
       $('.main').removeClass("flash");
    flash = !flash;
}, 10000);