JSFiddle - React, Tailwind, and code Playground

HTML

<div class="row-wrapper">
  <div class="col-wrapper-outer">
    <div class="arrow-wrapper">
      &darr;
    </div>
    <div class="col-wrapper">
      <div class="header">Please align tops.</div>
      <div class="contents">Let me grow.</div>
    </div>
  </div>
  <div class="col-wrapper-outer">
    <div class="arrow-wrapper">
      &darr;
    </div>
    <div class="col-wrapper">
      <div class="header">please align tops.</div>
      <div class="contents">Let me grow.
        <br>Please
        <br>align
        <br>bottoms.</div>
    </div>
  </div>
</div>

CSS

.row-wrapper {
  display: flex;
}

.col-wrapper-outer {
  display: flex;
  /* flex-wrap: wrap; */
  flex-direction: column; /* NEW */
}

.arrow-wrapper {
  width: 100%;
  text-align: center;
  font-size: 30px;
}

.col-wrapper {
  flex: 1; /* NEW */
  width: 100%;
  display: flex;
  flex-direction: column;
  border: 2px solid red;
  color: white;
}

.col-wrapper .header {
  background: blue;
}

.col-wrapper .contents {
  flex: 1 0 auto;
  background: green;
}