如何在较大的div内垂直和水平居中div？

<style>
    .parent {
        display: flex;
        justify-content: center;
        align-items: center;
        width: 100%;
        height: 400px; /* 假设父级div高度为400px */
        background-color: #f1f1f1;
    }

    .child {
        width: 200px;
        height: 200px;
        background-color: #ccc;
    }
</style>

<div class="parent">
    <div class="child"></div>
</div>

<style>
    .parent {
        position: relative;
        width: 100%;
        height: 400px; /* 假设父级div高度为400px */
        background-color: #f1f1f1;
    }

    .child {
        position: absolute;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%);
        width: 200px;
        height: 200px;
        background-color: #ccc;
    }
</style>

<div class="parent">
    <div class="child"></div>
</div>