绝对定位垂直居中
<style>
.bigbox{
width: 100px;
height: 100px;
background-color: red;
position: relative;
}
.smallbox{
width: 50px;
height: 50px;
background-color: blue;
position: absolute;
top:50%;
transform: translateY(-50%);
}
</style>
<body>
<div class="bigbox">
<div class="smallbox">
</div>
</div>
</body>
图片垂直居中
vertical-align: middle;