console 命令行工具 X clear

console

<div id="app">
    <div>1</div>
</div>

#app {
    width: 100vw;
    height: 100vh;
    background: #fff;
    display: table-cell;
    vertical-align: middle;
}

#app > div {
    margin: auto;
    background: red;
    width: 200px;
    height: 200px;
}