bootstarp container center code example
Example: bootstrap center
<div class="row h-100">
<div class="col-sm-12 my-auto">
<div class="card card-block w-25">Card</div>
</div>
</div>
<div class="row h-100">
<div class="col-sm-12 my-auto">
<div class="card card-block w-25">Card</div>
</div>
</div>