display bosstrap 4 code example

Example 1: visibility hidden bootstrap 4

<div class="visible">...</div>
<div class="invisible">...</div>

Example 2: is display-block a class

<span class="d-block p-2 bg-primary text-white">d-block</span>
<span class="d-block p-2 bg-dark text-white">d-block</span>