<style type="text/css"> 
body { 
margin-left: 0px; 
margin-top: 0px; 
margin-right: 0px; 
margin-bottom: 0px; 
background="../src/back.gif"; 
  } 
</style> 
<script language="JavaScript"> 
function formCheck() 
{ 
alert()
if(leaMsgBoard.oname.value==""){ 
alert("请输入你的姓名！"); 
leaMsgBoard.oname.focus(); 
return false; 
} 
if(leaMsgBoard.oclass.value==""){ 
alert("请输入你的班级！"); 
leaMsgBoard.oclass.focus(); 
return false; 
} 

if(leaMsgBoard.contact.value==""){ 
alert("请填入你的电子邮件！"); 
leaMsgBoard.contact.focus(); 
return false; 
} 
} 
</script> 

<form action="setMsg.jsp" method="post" name="leaMsgBoard" onsubmit="return formCheck();" > 
<table width="700" border="0" align="center" cellpadding="4" 1" bgcolor="#ebcellspacing="ebeb"> 
<tr> 
<td> 
  <br>姓名: <input type="text" name="oname" size="12"> 
  <p>班级: <input type="text" name="oclass" size="12"> </p> 
  <P>联系方式: <input type="text" name="contact" size="20"> </p> 
  <input type="submit" name="SubmitBtn" value="确认"> 
</td> </tr> </table> 
</form>

很简单的问题 把你的<style>拿到<script>标签外面即可 还有别以关键字命名