JSFiddle - React, Tailwind, and code Playground

HTML

<div id="image-form">
  <label for="url">Image URL</label>
  <input type="text" id="url" />
  <input type="button" value="Update" onclick="updateURL()" />
</div>

CSS

html, body {
  width: 100%;
  height: 100%;
}

body {
    background-size: cover;
    
    -ms-filter: 'progid:DXImageTransform.Microsoft.AlphaImageLoader(src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7", sizingMethod="scale")';
}

#image-form {
  display: inline-block;
  background: #fff;
  padding: 10px;
}

JavaScript

window.onload = function() {
  setBackground();
}

function updateURL() {
  var newURL = document.getElementById('url').value;
  setCookie('URL', newURL, 365);
  document.body.style.background = 'url('+newURL+') no-repeat';
  document.body.style.backgroundSize = 'cover';
  document.body.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = newURL;
  document.body.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").sizingMethod = 'scale';
}

function setBackground() {
  var URL = getCookie('URL');
  document.body.style.background = 'url('+URL+') no-repeat';
  document.body.style.backgroundSize = 'cover';
  document.body.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = URL;
  document.body.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").sizingMethod = 'scale';
}

function setCookie(c_name, value, exdays) {
  var exdate=new Date();
  exdate.setDate(exdate.getDate() + exdays);
  var c_value=escape(value) + ((exdays==null) ? "" : "; expires="+exdate.toUTCString());
  document.cookie=c_name + "=" + c_value;
}

function getCookie(c_name) {
  var c_value = document.cookie;
  var c_start = c_value.indexOf(" " + c_name + "=");

  if (c_start == -1)
    c_start = c_value.indexOf(c_name + "=");

  if (c_start == -1) {
    c_value = null;
  } else {
    c_start = c_value.indexOf("=", c_start) + 1;
    var c_end = c_value.indexOf(";", c_start);

    if (c_end == -1)
      c_end = c_value.length;

    c_value = unescape(c_value.substring(c_start,c_end));
  }
  return c_value;
}