bootstrap 4 center div

1<div class="row justify-content-center">
2  ...inner divs and content...
3</div>

1<div class="d-flex justify-content-start">...</div>
2<div class="d-flex justify-content-end">...</div>
3<div class="d-flex justify-content-center">...</div>
4<div class="d-flex justify-content-between">...</div>
5<div class="d-flex justify-content-around">...</div>

1<!-- Center columns in a Row -->
2<div class="row d-flex justify-content-center text-center">
3    <div class="col-4">
4        // Add Content
5    </div>
6    <div class="col-4">
7        // Add Content
8    </div>
9    <div class="col-4">
10        // Add Content
11    </div>
12</div>

1<div class="d-flex justify-content-center">...</div>

1<div class="my-auto">
2  ...inner divs and content...
3</div>