When you want to add some short messages via a modal window this handy script by Samuel Janes might come in handy. When you click on the button it pops up the modal window and reveals your message.
If you are having trouble with the pen, try the archived copy on GitHub
Button to Popup Snippet
See the Pen Daily UI #016 | Pop-Up / Overlay by Samuel Janes (@SamuelJanes) on CodePen.0