<div class="row d-flex flex-md-column"> code example
Example 1: bootstrap 4 center div
<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>
Example 2: ustify-content: flex-end; bootstrap
<div class="d-flex justify-content-end">...</div>