Flexbox-嵌套的父div在其内容可滚动时不会展开

.first {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
}

.second {
  display: flex;
  flex-direction: row;
  flex-wrap: nowrap; /*Forcing items to expand the parent*/
  flex: 0 1 100%;
  overflow-x: scroll;
  background-color: whitesmoke;
}

.second div {
  display: flex;
  flex: 0 0 25%;
}

<div class="first">
  <div class="second">
    <div>Item 1</div>
    <div>Item 2</div>
    <div>Item 3</div>
    <div>Item 4</div>
    <div>Item 5</div>
  </div>
</div>