HTML标签
<form> 标签
input placeholder（文本框里显示内容）
<body>标签
<style>
body{
margin:0;
}
</style>
<style>标签
display:bloce; //表示是块级标签，占整行
<DIV>标签
position:fixed absolut relative 区别
莫泰对话框：
遮罩层<div class="shade"></div>
添加层<div class="add-model"></div>
<style>
.shade{
position: fixed;
top:0;
right: 0;
left:0;
bottom: 0;
background: black;
opacity: 0.6;
z-index:101
}
.add-model{
position: fixed;
height: 300px;
width:400px;
top:100px;
left:50%;
border: 1px solid red;
background: white;
z-index:101;
margin-left: -200px;
}
</style>
