How to make a floating button

Hi all! I wonder what is the easiest way to make a floating button like in this page? The button with the phone icon that is fixed. If somebody just could help me step by step perhaps? I tried to look at this template in preview mode, but still does not have a clue.

http://risoto-template.webflow.io

I will explain as simple as possible.

Make the body of the page position relative

Add a new div to page

Make the div size 100px x 100px

Set div background to a bright colour so you can see it against the body

Set the div position absolute (to the body)

Set the div z index to 2

Absolute the position the div to bottom right

You can then add text etc and style as you want.

A simple button I created is shown below

Thanks @RoseWebStudio! Problem is its not possible to sett the body to position relative, that particular function shadowed?