1. 1996

   CSS level 1

   CSS1 becomes a W3C Recommendation. Styling moves out of the markup, but nothing moves yet.

2. 2007

   WebKit shows off transitions

   The WebKit team announces CSS transitions and transforms, letting property changes animate without script.

3. 2009

   First working drafts

   The W3C publishes the first drafts of CSS Transitions and CSS Animations, with keyframes as we know them today.

4. 2016

   IntersectionObserver ships

   Chrome 51 ships IntersectionObserver, so pages can react to visibility without listening to every scroll event.

5. 2017

   prefers-reduced-motion

   Safari 10.1 is the first browser to support the media query, giving people a way to turn motion down.

6. 2019

   Observer everywhere

   Safari 12.1 adds IntersectionObserver, and every major browser can now run this kind of reveal natively.