实际图：600px*500px
效果图：
代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<style>
* {
margin: 0px;
padding: 0px;
}
ul,
li {
list-style-type: none;
}
.box {
width: 1200px;
margin: 30px auto;
display: table;
}
.list li {
position: relative;
float: left;
width: 300px;
height: 300px;
background-repeat: no-repeat;
background-size: cover;
background-position: center center;
}
.list li:before {
content: '';
position: absolute;
width: 100%;
height: 100%;
border: 1px solid red;
}
</style>
<body>
<div class="box">
<ul class='list'>
<li style="background-image: url(timg.jpeg)"></li>
<li style="background-image: url(timg.jpeg)"></li>
<li style="background-image: url(timg.jpeg)"></li>
<li style="background-image: url(timg.jpeg)"></li>
</ul>
</div>
</body>
</html>
总结：
主要代码：
background-size: cover;
background-repeat: no-repeat;
background-position: center center;