JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <a id="button" href="#">REGISTER</a>
</div>
<br>
<br>
<div id="item">
    <iframe id="regFrame" src="http://placekitten.com/g/760/550" embedded="true" width="760" height="550" frameborder="0" marginheight="0" marginwidth="0">
        Loading
    </iframe>
</div>

CSS

#regFrame{
    display: none;
}

JavaScript

$('#button').click(function(){
    //$('#regFrame').show();
    //$('#regFrame').toggle(); //To hide the iframe when the button is clicked again
    //$('#regFrame').show(500); //To fade in the iframe
    $('#regFrame').toggle(500); //To fade the iframe in and out
});