JSFiddle - React, Tailwind, and code Playground

HTML

<div id="form">
  <p>fill stuff out here</p>
</div>

<div class="loading-bar" id="loading-bar">
  <img src="https://upload.wikimedia.org/wikipedia/commons/2/2c/Rotating_earth_%28large%29.gif" height="100" width="100">
</div>

<input onclick="show_loading_bar()" type="submit">

CSS

.loading-bar {
  display: none;
}

JavaScript

function show_loading_bar() {
	document.getElementById("form").style.display = "none";
  document.getElementById("loading-bar").style.display = "flex";
}