<div class="container">
<div class="row">
<div class="col-md">col-sm</div>
<div class="col-md">col-sm</div>
<div class="col-md">col-sm</div>
</div>
</div>.row > div {
outline: 1px solid purple;
padding: 10px;
}
.center {
text-align: center;
}