t item to have a width of 75px.)">

<style>
  .item {
    /* Remove min-height so we don't have to think about it. */
    min-height: 0px;
    flex: 0 0 100px;
    outline: 1px solid;
  }

  .grandchild {
    width: 75px;
    float: left;
  }
</style>

<div
  style="display: flex; flex-flow: column wrap; width: max-content; height: 100px; background: green; position: relative;"
  data-expected-width="250">
  <div class="item" style="width: 100px;"></div>
  <div class="item" style="width: fit-content;" data-