At the end of the page, before the closing </body> tag, plug in jQuery and parts-ui.min.js file. Install it locally in your project, or hook up from the server:
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js" defer="defer"></script>
<script src="https://partsui.com/files/release/js/partsui.min.js" defer="defer"></script>
jQuery library is not included, thus should be downloaded individually
Gets <body> after full page load
Gets <body> if the page is opened from a touch device
.scroll-direction-up
.scroll-direction-down
Gets <body> depending on which direction the page is scrolled
scroll-direction-up
scroll-direction-down
.document-has-scroll
.document-without-scroll
Gets the document <body>, depending on whether the page has a vertical scrollbar