why these outcommented selection methods dont work?

why these outcommented selection methods dont work?

these outcommented selection methods dont work,
i cant see why
it was about just experimenting
  2. <!DOCTYPE html>
  3. <html>
  4. <head>
  5. <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js">
  6. </script>
  7. <script>
  8. $(document).ready(function(){
  9.   $("button").click(function(){
  10.     $("#div1").fadeIn();
  11.     $("#div2").fadeIn("slow");
  12.     $("#div3").fadeIn(3000);
  13.     $("#div3").css('background-color','blue');
  14.   });
  15. });


  18. $(document).ready(function(){
  19.   $("#div1").click(function(){
  20.     $('.effekt :nth-child(2)').prev().css('background-color','purple');
  21.     
  22. ////////////following selection methods dont work, why?
  23.  //   $('.effekt :nth-child(3)').prev().css('background-color','orange'); //but previous one is the same!
  24.  //   $('.effekt :nth-child(2)').css('background-color','orange');
  25.  //   $('#div3').prev().css('background-color','orange');
  26.  //   $(this).next().css('background-color','orange');
  27.  //   $('#div1').next().css('background-color','orange');
  28. //---------------------------------------------------------
  29.     $("#div2").css('background-color','grey');
  30.     $("#div3").css('background-color','gold');
  31.  });
  32. });


  35. $(document).ready(function(){
  36.   $("#rejto").click(function(){
  37.     $("body .effekt div").hide();
  38. }); });
  39. </script>
  40. </head>

  42. <body>
  43. <p>fadeIn()-hide()-css</p>
  44. <button>click to show</button>
  45. <br><br>

  47. <div class="effekt">
  48. <div id="div1" style="width:80px;height:20px;display:none;background-color:red;"></div><br>
  49. <div id="div2" style="width:80px;height:20px;display:none;background-color:green;"></div><br>
  50. <div id="div3" style="width:80px;height:20px;display:none;background-color:blue;"></div><br>
  51. </div>
  52. <br>
  53. <button id="rejto">hide all</button>
  54. </body>
  55. </html>