SOURCE

<div class="parent place-items-center">
    <div class="box"></div>
</div>

html, body {
    height: 100%;
}

.parent {
 width: 100%;
 height: 100%;
 background: lightblue;
}

.box {
    padding: 10px;
    background: goldenrod;
}

/* 超级居中 */
.place-items-center {
    display: grid;
    place-items: center;
}