gecko-dev/browser/devtools/styleeditor/test/media-rules.css

@media not all {
  div {
    color: blue;
  }
}

@media all {
  div {
    color: red;
  }
}

div {
  width: 20px;
  height: 20px;
  background-color: ghostwhite;
}

@media (max-width: 400px) {
  div {
    color: green;
  }
}