ref. https://codepen.io/isladjan/pen/abdyPBw
animate tab bar
https://codepen.io/abxlfazl/pen/VwKzaEm
Fade in Background Image Only after Loading Fully
https://jsfiddle.net/nud2bfb1/4/
https://freefrontend.com/css-animated-backgrounds/
https://www.sliderrevolution.com/resources/css-animated-background/
https://codepen.io/tonkotsuboy/pen/zJbKNN