You can add the following code to your site within [Website Management > Website Settings > Code Injection] to the Extra Header Code Injection area.
NOTE: You can use the values "top-left", "top-right", "bottom-left" or "bottom-right" to control where the button will appear for your visitors.
How will this button appear for my visitors and can I style how it will display?
The notification is a simple two button overlay but unfortunately it's not possible to modify the style of the button. You can however use different variables to modify the position of the button. See below for an example of how this will display.