[Bootstrap] Grid 의 vertical-align

<!--- vertical-align for row --->
<div class="container">
    <div class="row align-items-center">
        <div class="col-12 text-center">Content</div>
    </div>
</div>

<!--- vertical-align for column --->
<div class="container">
    <div class="row">
        <div class="col-12 align-self-center text-center">Content</div>
    </div>
</div>

<!--- vertical-align for column --->
<div class="container">
    <div class="row">
        <div class="col-12 my-auto text-center">Content</div>
    </div>
</div>