JSFiddle - React, Tailwind, and code Playground

HTML

<div class="login-signup-page">
<div class="login-signup">Sample Text</div>
</div>

CSS

.login-signup-page {
    position:absolute;
    left:0;
    top:0;
    height:100%;
    width:100%;
    background:grey;
}

.login-signup {
    width:100%;
    background:white;
    position:absolute;
    top:50%;
}

JavaScript

$(document).ready(function() {
   $('.login-signup').css('margin-top', $('.login-signup').height()*-1 + 'px'); 
});