bootstrap4 d-flex text center code example
Example 1: bootstrap justify-content-center for md
<div class="row justify-content-md-center"></div>
Example 2: bootstrap justify-content-center for lg
<div class="row justify-content-lg-center"><div>
<div class="row justify-content-md-center"></div>
<div class="row justify-content-lg-center"><div>