SOURCE

console 命令行工具 X clear

                    
>
console
<div class="parent">
    <div class="child"></div>
</div>
.parent {
    width: 200px;
    height: 200px;
    border: 1px solid;
}

.parent::before {
    vertical-align: middle;
    content: "";
}

.child {
    display: inline-block;
    width: 100px;
    height: 100px;
    vertical-align: middle;
    background-color: #699;
}