As the web became more interactive, there was an increased desire to animate elements on webpages. Animations are a powerful tool for increasing visual interest and also conveying information. Consider the Apple sign-in dialog, which on an incorrect username/password combination shakes back and forth briefly, mimicking a human’s head shaking.

Early animations in the web relied on using JavaScript to change properties of elements on the page. While these techniques are still used, they are increasingly supplanted by new CSS rules that are easier to write and provide more precise control.