1.水平居中的 margin：0 auto;
<style>
*{
padding: 0;
margin: 0;
}
.box{
width: 300px;
height: 300px;
border: 3px solid red;
/*text-align: center;*/
}
img{
display: block;
width: 100px;
height: 100px;
margin: 0 auto;
}
</style>
<!--html-->
<body>
<div class="box">
</div>
</body>
2.水平居中 text-align：center;
<style>
*{
padding: 0;
margin: 0;
}
.box{
width: 300px;
height: 300px;
border: 3px solid red;
text-align: center;
}
img{
display: inline-block;
width: 100px;
height: 100px;
/*margin: 0 auto;*/
}
</style>
<!--html-->
<body>
<div class="box">
</div>
</body>
3.水平垂直居中 定位和需要定位的元素的margin减去宽高的一半（需要知道宽高）
<style>
*{
padding: 0;
margin: 0;
}
.box{
width: 300px;
height: 300px;
background:#e9dfc7;
border:1px solid red;
position: relative;
}
img{
width: 100px;
height: 150px;
position: absolute;
top: 50%;
left: 50%;
margin-top: -75px;
margin-left: -50px;
}
</style>
<!--html -->
<body>
<div class="box" >
</div>
</body>
4.水平垂直居中 定位和margin:auto;（不需要知道宽高）
<style>
*{
padding: 0;
margin: 0;
}
.box{
width: 300px;
height: 300px;
background:#e9dfc7;
border:1px solid red;
position: relative;
}
img{
width: 100px;
height: 100px;
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
margin: auto;
}
</style>
<!--html -->
<body>
<div class="box" >
</div>
</body>
5.水平垂直居中绝对定位和transfrom（不需要知道宽高）
<style>
*{
padding: 0;
margin: 0;
}
.box{
width: 300px;
height: 300px;
background:#e9dfc7;
border:1px solid red;
position: relative;
}
img{
width: 100px;
height: 100px;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%,-50%);
}
</style>
<!--html -->
<body>
<div class="box" >
</div>
</body>
