console 命令行工具 X clear

console

$("p").hide()
$('p').show()
$("p:first").hide()
$("ul li:first").hide()
$("ul li:first-child").hide()
$("#showBtn").click(function(){$("ul li:first-child").show();});
$("#hideBtn").click(function(){$("ul li:first-child").hide();});

<h1>heading</h1>
<p>paragraph</p>
<p>paragraph1</p>
<ul>
  <li>a1</li>
  <li>a2</li>
</ul>
<ul>
  <li>b1</li>
  <li>b2</li>
</ul>

<button id="showBtn">显示</button>
<button id="hideBtn">隐藏</button>

p
{
  color:red;
}