I think you’d want to wrap the entire site in a container so you could style it.
1. Open your container in the Before Header hook in GP Hooks:
<div class="whole-site-container">
2. Close your container in the wp_footer hook:
</div>
3. Add CSS to your new container:
.whole-site-container {
padding: 30px;
background-color: rgba( 255, 255, 255, 0.3 );
}