Answers for "center flex-column items in bootstrap"

bootstrap flex align

<div class="d-flex justify-content-start">...</div>
<div class="d-flex justify-content-end">...</div>
<div class="d-flex justify-content-center">...</div>
<div class="d-flex justify-content-between">...</div>
<div class="d-flex justify-content-around">...</div>

bootstrap justify-content-center for md

<div class="row justify-content-md-center"></div>