-width="40" data-expected-height="40">
    </div>
    <br>

    <!-- Row 4: max main-size OR max cross-size, or both -->
    <div class="flexbox">
      <img src="support/solidblue.png" style="max-width: 10px" data-expected-width="10" data-expected-height="10">
    </div>
    <div class="flexbox">
      <img src="support/solidblue.png" style="max-height: 10px" data-expected-width="40" data-expected-height="10">
    </div>
    <div class="flexbox">
      <img src="support/solidblue.png" style="max-width: 10p