I tried centering a div within another div. I saw Manoj Kumar's response to this question. But it's not working.
<div class="row">
  <div class="col-sm-9">
    <div class="contAin">
        <div class="tile">Some Content</div>
    </div>
</div>
</div>
and the css
.tile {
  margin-bottom: 30px;  
  width: 80%;
}
.contAin {
  display: flex;
  justify-content: center;
}
The inner div is just aligning itself to the left.
 
     
     
     
     
     
    