<!DOCTYPE html>
<html>
<head>
<style>
table,th,td
{
border:1px solid black;
}
</style>
</head>
<body>
<table>
<colgroup>
<col id="myCol">
<col style="background-color:yellow">
</colgroup>
<tr>
<th>ISBN</th>
<th>Title</th>
<th>Price</th>
</tr>
<td>3476896</td>
<td>My first HTML</td>
<td>$53</td>
<td>5869207</td>
<td>My first CSS</td>
<td>$49</td>
</table>
<p>请点击按钮，把前两列的背景色设置为红色。</p>
<p id="demo"></p>
<button onclick="myFunction()">试一下</button>
<script>
function myFunction()
document.getElementById("myCol").span="2";
document.getElementById("myCol").style.backgroundColor="red";
</script>