<html>
<head>
<style>
table,th,td
{
border:1px solid black;
}
</style>
</head>
<body>
<table>
<colgroup id="myColgroup"></colgroup>
<tr>
<th>ISBN</th>
<th>Title</th>
<th>Price</th>
</tr>
<tr>
<td>3476896</td>
<td>My first HTML</td>
<td>$53</td>
</tr>
<tr>
<td>5869207</td>
<td>My first CSS</td>
<td>$49</td>
</tr>
</table>
<p>点击按钮设置表格中前两列的颜色为红色</p>
<p id="demo"></p>
<button onclick="myFunction()">点我</button>
<script>
function myFunction()
{
document.getElementById("myColgroup").span="2";
document.getElementById("myColgroup").style.backgroundColor="red";
}
</script>
</body>
</html>