                        課程
                    
                        /前端開發
                        
                            /JavaScript
                        
                        /JavaScript入門篇

怎么沒效果啊

<!DOCTYPE?HTML>
<html>
<head>
<meta?http-equiv="Content-Type"?Content="text/html;?charset=utf-8"?/>
<title>javascript</title>
<style?type="text/css">
body{font-size:12px;}
#txt{
????height:400px;
????width:600px;
????border:#333?solid?1px;
????padding:5px;}
p{
????line-height:18px;
????text-indent:2em;}
</style>
</head>
<body>
??<h2?id="con">JavaScript課程</H2>
??<div?id="txt">?
?????<h5>JavaScript為網頁添加動態效果并實現與用戶交互的功能。</h5>
????????<p>1.?JavaScript入門篇，讓不懂JS的你，快速了解JS。</p>
????????<p>2.?JavaScript進階篇，讓你掌握JS的基礎語法、函數、數組、事件、內置對象、BOM瀏覽器、DOM操作。</p>
????????<p>3.?學完以上兩門基礎課后，在深入學習JavaScript的變量作用域、事件、對象、運動、cookie、正則表達式、ajax等課程。</p>
??</div>
??<form>
??<!--當點擊相應按鈕，執行相應操作，為按鈕添加相應事件-->
????<input?type="button"?value="改變顏色"?onClick="one()">??
????<input?type="button"?value="改變寬高"?onClick="two()">
????<input?type="button"?value="隱藏內容"?onClick="three()">
????<input?type="button"?value="顯示內容"?onClick="four()">
????<input?type="button"?value="取消設置"?onClick="five()">
??</form>
??<script?type="text/javascript">
//定義"改變顏色"的函數
????function?one(){
????var?my?=?document.getElementById("txt");
???????my.style.color="red";
???????my.style.backgroundColor="blue";
????}

//定義"改變寬高"的函數
????????function?two?(){
????????var?my?=?document.getElementById("txt");
????????my.style.width?="400px";
???????my.style.height=?"200px";
????????}

//定義"隱藏內容"的函數
?????function?three(){
??????????var?yincang?=document.getElementById("txt");
??????????yincang.style.display="none";
?????}
//定義"顯示內容"的函數
??????????function?four(){?
???????????var?huifu?=document.getElementById("txt");
?????????huifu.style.display="block";
??????????}

//定義"取消設置"的函數
?????????function?five(){
?????????if(confirm("確定要取消設置嗎？”)){
?????????????var?clear?=document.getElementById("txt");
?????????????clear.style.color="#000";
?????????????clear.style.backgroundColor="#fff";
?????????????clear.style.width="600px";
?????????????clear.style.height="400px";
?????????????clear.style.display="block";
??????????}
?????????}

??</script>
</body>
</html>