如何将div放在右边？

<style>
    .right-div {
        float: right;
    }
</style>
<div class="right-div">这是右边的div</div>

<style>
    .right-div {
        position: absolute;
        top: 0;
        right: 0;
    }
</style>
<div class="right-div">这是右边的div</div>

<style>
    .parent-container {
        display: flex;
        justify-content: flex-end;
    }
</style>
<div class="parent-container">
    <div class="right-div">这是右边的div</div>
</div>