Plugin, beproefd en in gebruik (check feb 2019)

WP Slidenotes

Slidenotes lets you add fancy sliding notes into your wordpress posts, pages or text widgets using a simple and customizable shortcode.

Shortcode: [slidenote text="Click me!"]The Slidenote content goes here[/slidenote]The shortcode will create a slidenote, also it will render the trigger text, which will make the slidenote slide-in into the content when clicked or hovered.