JSFiddle - React, Tailwind, and code Playground

HTML

<div>Div One
    <div>Div Two</div>
</div>
<button>FULL SCREEN</button>

CSS

div {
    background: gold;
    padding: 20px;
    height: 500px;
    width: 100px;
}
div > div {
    background: blue;
}
body {min-height: 3000px;}
button {
    position: absolute;
    top: 50px;
    left: 100px;
}

JavaScript

$(':button').click(function() {
  $('div > div').css({
      position:'absolute', //or fixed depending on needs 
      top: $(window).scrollTop(), // top pos based on scoll pos
      left: 0,
      height: '100%',
      width: '100%'
  });
});