Setup different icons for cards (button-card etc.)

How can i setup special icons like that

for my button-cards and something?
Can i use base64 codes for icons or something?

I saw that on this post on reddit: https://www.reddit.com/r/homeassistant/comments/pqwyxb/new_dashboard_for_my_wall_mounted_tablet/

But i dont know how to setup that cool icons