如何在相对父级的填充顶部垂直对齐div

<style>
    .parent {
        display: flex;
        align-items: flex-start;
    }
</style>

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

<style>
    .parent {
        position: relative;
    }
    .child {
        position: absolute;
        top: 0;
    }
</style>

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

<style>
    .parent {
        position: relative;
    }
    .child {
        position: absolute;
        margin-top: 0;
    }
</style>

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