<!DOCTYPE html>
<html>
<head>

<div class="container">
  <div class="box">A</div>
  <div class="box tall">B</div>
  <div class="box">C</div>
</div>



<style type="text/css">
  .container {
  display: flex;
  align-items: flex-end; /* না দিলে Stretch হবে */
  height: 200px;
  background: #eee;
}

.box {
  width: 50px;
  height: 50px;
  background: lightblue;
  margin: 5px;
}

.tall {
  height: 120px;
  background: skyblue;
}


</style>

</body>
</html>