Add a Slideshow above Header

Homepage

First, you add a slideshow section to Homepage

Next, add this code to Page Header Code Injection and click Save

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.0/jquery.min.js"></script>
<script>
jQuery(document).ready(function($){
  $('article>section:first-child').insertBefore('header#header');
})
</script>
<style>
header#header {
   position: sticky !important;
  transform: Unset !important;
}
div#siteWrapper>section {
    padding: 0px !important;
    z-index: 999999 !important;
}
</style>

The result is like below

All Pages

You add a slideshow section to all pages

Next, add this code Code Injection> Footer and click Save

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.0/jquery.min.js"></script>
<script>
jQuery(document).ready(function($){
  $('article>section:first-child').insertBefore('header#header');
})
</script>
<style>
header#header {
   position: sticky !important;
  transform: Unset !important;
}
div#siteWrapper>section {
    padding: 0px !important;
    z-index: 999999 !important;
}
</style>

You will have a result like this