code: function atcustommedia() {
      var pos = position();
      var m = match(/^@custom-media (--[^\s]+) *([^{;]+);/);
      if (!m) return;
  
      return pos({
        type: 'custom-media',
        name: trim(m[1]),
        media: trim(m[2])
      });
    }
docs: Parse custom-media.