Support for ::before and ::after pseudo elements?

[RedHatter]

Would it be possible to support the ::before and ::after pseudo elements? I would expect the code below to show a red rectangle in the center of the screen ... but the pseudo element is not positioned/styled.

#content {
  width: == 200;
  height: == 200;
  center: == ::window[center];
}

#content::before {
  content: ' ';
  background-color: red;
  width: == #content[width];
  height: == #content[height];
}