fix flex boootstrap code example
Example 1: flex wrap bootstrap
<div class="d-flex flex-wrap">...</div>
Example 2: Bootstrap 4 Flex
<div class="d-flex p-3 bg-secondary text-white">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>