Blank WordPress – Cannot see site or login!

Hello,

I added a CSS code to the bottom of the functions.php section in the editor. Now, my site comes up completely blank. When I try to login to my wp-admin site, it’s a blank screen too. The CSS code that I entered was from the Instagram plugin site: https://smashballoon.com/snippet/change-the-number-of-columns-for-small-screens/