Bootstrap CSS class .flex-*-grow-1

<div class="d-flex text-white">
  <div class="p-2 flex-grow-1 bg-primary">Flex item</div>
  <div class="p-2 bg-success">Flex item</div>
  <div class="p-2 bg-primary">Third flex item</div>
</div>

<div class="d-flex text-white mt-1">
  <div class="p-2 flex-sm-grow-1 bg-danger">Flex item</div>
  <div class="p-2 flex-md-grow-1 bg-warning">Flex item</div>
  <div class="p-2 flex-lg-grow-1 bg-danger">Flex item</div>
  <div class="p-2 flex-xl-grow-1 bg-warning">Flex item</div>
</div>