['atruler', 
  ['atkeyword', 
    ['ident', '-webkit-keyframes']], 
  ['atrulerq', 
    ['s', ' '], 
    ['ident', 'pulsate'], 
    ['s', ' ']], 
  ['atrulers', 
    ['ruleset', 
      ['selector', 
        ['simpleselector', 
          ['percentage', 
            ['number', '0']], 
          ['s', ' ']]], 
      ['block', 
        ['declaration', 
          ['property', 
            ['ident', 'opacity']], 
          ['value', 
            ['s', ' '], 
            ['number', '.5']]]]], 
    ['ruleset', 
      ['selector', 
        ['simpleselector', 
          ['percentage', 
            ['number', '50']], 
          ['s', ' ']]], 
      ['block', 
        ['declaration', 
          ['property', 
            ['ident', 'opacity']], 
          ['value', 
            ['s', ' '], 
            ['number', '1']]]]], 
    ['ruleset', 
      ['selector', 
        ['simpleselector', 
          ['percentage', 
            ['number', '100']], 
          ['s', ' ']]], 
      ['block', 
        ['declaration', 
          ['property', 
            ['ident', 'opacity']], 
          ['value', 
            ['s', ' '], 
            ['number', '.5']]]]]]]