CSS has specifications

CSS 2.1, represented by an image of a document with many lines of text: hello, this is how max-width works in excruciating detail

there used to be just one specification

Illustration of a smiling stick figure with curly hair.

person: it’s called “CSS 2” and I still like to reference it to learn the basics

today, every CSS feature has its own specification

you can find them all at https://www.w3.org/TR/CSS/

there are dozens of specs, for example: colors, flexbox, and transforms

major browsers usually obey the spec

but sometimes they have bugs

Illustration of a happy little caterpillar-type bug.

browser, represented by a box with a smiley face: oops, I didn’t quite implement that right…

levels

CSS versions are called “levels”.

new levels only add new features. They don’t change the behaviour of existing CSS code

new features take time to implement

https://caniuse.com
(The URL is surrounded by little hearts and stars)

can tell you which browser versions support a CSS feature