<div class="container">
    <div class="box">

    </div>
    </div>

.container{
    width:600px;
    height:400px;
    border:1px solid blue;
    display: flex;
    justify-content:center;
    align-items:center;
    }
    .box{
    width:200px;
    height:100px;
    border:1px red solid;

<div class="items">
    <div class="item">1</div>
    <div class="item">23</div>
    <div class="item">4</div>
    </div>