JavaScript动态修改元素样式：内联style与外部CSS的两种实现方式

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
  <title>Change.html</title>
  <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  
  <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
 <script language="javascript">
   function test4(event) {
	  if(event.value == "黑色") {
	   //获取div1
	   var div1 = document.getElementById('div1');
	   div1.style.backgroundColor="black";
	  }
	  if(event.value == "红色") {
	   //获取div1
	   var div1 = document.getElementById('div1');
	   div1.style.backgroundColor="red";
	  }
	 }
 </script>
</head>
<body>
 <div id="div1" style="width:400px; height:300px; background-color:red;">div1</div>
 <input type="button" value="黑色" onclick="test4(this)"/>
 <input type="button" value="红色" onclick="test4(this)"/>

 </body>
</html>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
  <title>Change1.html</title>
  <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  
  <link rel="stylesheet" type="text/css" href="css/Change.css">
 <script language="javascript">
   function test4(event) {
	 //获取样式表中所有class选择器都获得
	 var ocssRules = document.styleSheets[0].rules;
	 //从ocssRules中取出你希望的class
	 var style1 = ocssRules[0];
	 if(event.value == "黑色") {
	   //window.alert(style1.style.backgroundColor);
	   style1.style.backgroundColor="black";
	 }else if(event.value == "红色") {
	   style1.style.backgroundColor="red";
	 }
	 
	 }
  </script>
</head>
<body>
 <div id="div1" class="style1">div1</div>
 <input type="button" value="黑色" onclick="test4(this)"/>
 <input type="button" value="红色" onclick="test4(this)"/>

 </body>
</html>