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Bootstrap class: .order-*-#

<div class="d-flex flex-nowrap">
  <div class="order-8 p-2">First flex item</div>
  <div class="order-12 p-2">Second flex item</div>
  <div class="order-3 p-2">Third flex item</div>
</div>

<!-- responsive variations -->
<div class="order-sm-3">Flex item</div>
<div class="order-md-3">Flex item</div>
<div class="order-lg-3">Flex item</div>
<div class="order-xl-3">Flex item</div>

Preview

First flex item
Second flex item
Third flex item