Adding custom code onto homepage

I’ve developed a simple visualization using HTML/CSS/Javascript and D3 library locally and want to have it display on the homepage of my Omeka site. Currently, my homepage is a Simple Page (created using Simple Pages plugin) and I want to retain the theme and navigation bar but also add my custom HTML/Javascript, to display my visualization in the empty area beneath the nav bar.

Is there a way to include custom HTML/Javascript on a Simple Page? If not, is there a way to include custom HTML/Javascript on any page while retaining the selected Omeka theme, nav bar, and other core elements I want to remain unaffected?

You can disable HTML filtering and then put whatever HTML you want in a Simple Page.

Otherwise, you can add to the theme directly (common/header.php most likely if you want to add to every page). You can also add to just the Simple Pages view, but it is slightly more complicated: you need to copy the Simple Pages plugin file views/public/page/show.php to simple-pages/page/show.php in your theme, then you can edit it.