nested css rules [duplicate]

Answer 1

That is not valid standard CSS, but it's an example of nesting class declarations using Sass/SCSS or LESS and I believe other CSS extensions out there, which expand it to something like this (which is valid CSS), before serving it to the browser to use:

div.a {
  color: red;
}

div.a div.b {
  /* Inherits color from div.a */
  font-weight: bold;
}

Answer 2

You can nest rules with SASS, http://sass-lang.com/

Maybe that was it?

Answer 3

What you are probably referring to is LESS.

The example, you gave is not valid CSS, but is valid with LESS. LESS will "compile" the nested CSS and convert it to something which is valid CSS.

Answer 4

Seems there is a proposal over at https://tabatkins.github.io/specs/css-nesting/

but I can't find the status of it