How to properly arrange the sides in flexbox?

Question

css

Good afternoon, help me make responsive blocks in flexbox.

Answer 1

https://codepen.io/ViktoriaKorneva/pen/jOOyXEj

Answer 2

<div class="flex">
  <div class="block">1</div>
  <div class="block">
    <div class="flex column">
      <div class="block">2</div>
      <div class="block">3</div>
    </div>
  </div>
</div>

<style>
  .flex {
    display: flex;
  }

  .column {
    flex-direction: column;
  }
  
/* для демо */
  .block {
    min-width: 100px;
    min-height: 100px;
    background-color: #eee;
    display: flex;
    align-items: center;
    justify-content: center;
  }

</style>