View the page source to see the code
Concepts on W3Schools
https://www.w3schools.com/css/css3_transitions.asp
https://www.w3schools.com/cssref/css3_pr_animation-keyframes.asp
https://www.w3schools.com/css/css3_animations.asp
https://www.w3schools.com/cssref/css3_pr_animation-direction.asp