jQuery: Select the first of a set of elements with p:first

This is paragraph 1.

This is paragraph 2.

This is paragraph 3.

This is paragraph 4.

The Code START

  
  <script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script>
    <script type="text/javascript">
      function setStyle1() {
         $('p:first').css("font-style", "italic");
      }
      
      function setStyle2() {
         $('p:last').css("font-weight", "bold");
      }
      
      function resetStyle() {
        $('p:first').css("font-style", "normal");
        $('p:last').css("font-weight", "normal");
      }
    </script>
    
    <style type="text/CSS">
        <!--
        .code { color: red; }
        .back { background-color: yellow; }
        -->
    </style>
  </head>

  <body>
  <h1>Select the first of a set of elements with p:first</h1>
  <div>
  <p>This is paragraph 1.</p>
  <p>This is paragraph 2.</p>
  <p>This is paragraph 3.</p>
  <p>This is paragraph 4.</p>
  </div>
  <form action="">
   <input type = "button" value="Style first paragraph" onclick="setStyle1()"></input>
   <input type = "button" value="Style last paragraph" onclick="setStyle2()"></input>
   <input type = "button" value="Undo Styles" onclick="resetStyle()"></input>
  </form>