CSS & the W3C standards

CSS Standards & Versions

CSS evolves through modules, not "CSS5".

No single version

CSS3 was a marker; nowadays browsers ship CSS modules, each has its own level. There is no "CSS 4".

• colors module level 5.
• flexbox module level 1.1...

Who writes it

• W3C: the standards body (recommendations).
• WHATWG: shared web platform specs.

Support checking

@supports checks feature support:

@supports (display: grid) {
  .grid { display: grid; }
}
@supports not (display: grid) {
  .grid { display: block; }   /* fallback */
}

Browser support

• Meaning "baseline" = supported across majors (MDN baseline badge).
• Always check MDN/caniuse for new features.

TL;DR

• CSS is versioned per-module, not as one big version.
• W3C + browser engines decide.
• Use @supports for feature tests.
• Check baseline support before shipping new props.