c、after()和insertAfter() 在现存元素的外部，从后面插入元素
输出结果：
d、before()和insertBefore() 在现存元素的外部，从前面插入元素
输出结果：
3、删除节点
$(selector).remove();
4、to do list（计划列表）实例
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<link rel="stylesheet" href="../css/reset.css" rel="external nofollow" rel="external nofollow" >
<style>
.con{
width:360px;
margin:30px auto;
}
.con > h3{
margin-bottom:15px;
}
.con input{
width:290px;
height:30px;
}
.con button{
width:60px;
height:34px;
border:0;
}
.con ul li{
display: flex;
margin-top:15px;
border-bottom:1px solid #ccc;
justify-content: space-between;
}
.con li p{
/*清除a元素之间的间隙*/
font-size:0;
}
.con li p a{
color:#1b5fdd;
font-size:16px;
margin-left:10px;
}
/*弹框样式*/
.pop_con{
position:fixed;
top:0;
right:0;
bottom:0;
left:0;
background:#000;
display: none;
}
.pop{
width:400px;
height:220px;
position:absolute;
left:50%;
margin-left:-200px;
top:50%;
margin-top:-150px;
background:#fff;
}
.pop .pop_title{
padding:15px;
display: flex;
justify-content: space-between;
}
.pop .pop_title a{
width:36px;
height:36px;
line-height:36px;
border-radius:50%;
background:#c7254e;
color:#fff;
text-align: center;
position:absolute;
top:-18px;
right:-18px;
transition: all 1s ease;
}
.pop_title h3{
letter-spacing: 2px;
font-weight: normal;
}
.pop_title a:hover{
transform: rotate(360deg);
}
.pop_message{
height:110px;
line-height:110px;
text-align: center;
}
.pop_confirm{
height:36px;
text-align: center;
}
.pop_confirm button{
height:36px;
line-height: 36px;
padding:0 15px;
