1 通过background-position
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>background-position</title>
<style>
div
{
height:40px;
width:40px;
background-color:blue;
background-image:url('https://www.runoob.com/try/smiley.gif');
background-repeat:no-repeat;
background-position:center
}
</style>
</head>
2 使用img标签然后居中行内元素img标签，不使用background-image属性