Add #to-top fade in to #contact-button

Hello,

I would like for the contact ‘envelope’ button have the same ‘fading’ behaviour as the to-top ‘arrow’ button on the right side of the theme, where the arrow is hidden until you scroll down the below. How can I copy the ‘fade’ behaviour of the ID #to-top over to #contact-button.

I would like for both right side buttons to appear after you scroll down the page, but be hidden at the top of the page.

Can you please advise as to how to accomplish this behaviour.

Thank you,

Landon