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Bootstrap class: .align-content-*-start

<div class="d-flex flex-wrap align-content-start">
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
  ...
</div>

<!-- responsive variations -->
<div class="d-flex align-content-sm-start">...</div>
<div class="d-flex align-content-md-start">...</div>
<div class="d-flex align-content-lg-start">...</div>
<div class="d-flex align-content-xl-start">...</div>

Preview

Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item
Flex item