[解決済み] 最後のフレックスアイテムをコンテナの最後に配置する

.container {
  display: flex;
  flex-direction: column;
  outline: 1px solid green;
  min-height: 400px;
  width: 100px;
  justify-content: flex-start;
}
p {
  height: 50px;
  background-color: blue;
  margin: 5px;
}

<div class="container">
  <p></p>
  <p></p>
  <p></p>
  <p class="end"></p>
</div>

.container {
  display: flex;
  flex-direction: column;
  border: 1px solid #000;
  min-height: 200px;
  width: 100px;
}
p {
  height: 30px;
  background-color: blue;
  margin: 5px;
}
p:last-of-type {
  margin-top: auto;
}

<div class="container">
  <p></p>
  <p></p>
  <p></p>
</div>

.container {
  display: flex;
  width: 100%;
  border: 1px solid #000;
}
p {
  height: 50px;
  width: 50px;
  background-color: blue;
  margin: 5px;
}
p:last-of-type {
  margin-left: auto;
}

<div class="container">
  <p></p>
  <p></p>
  <p></p>
  <p></p>
</div>