Fullpage slider into the background

If your template/theme doesn’t have anything else in there, then you could put your slider into the background to be in a fixed position behind everything with this code, just put it right after the <body> part of your website:

Joomla

probably into the index.php file of the template

<div style="position:fixed;top:0;bottom:0;left:0;right:0;z-index:-1;">
<jdoc:include type="modules" name="bgsliderposition" />
</div>
WordPress

probably into the header.php file of the theme

<div style="position:fixed;top:0;bottom:0;left:0;right:0;z-index:-1;">
<?php echo do_shortcode('[smartslider3 slider=16]'); ?>
</div>