set>
<fieldset>
  <legend id=legend-center>center</legend>
</fieldset>
<fieldset>
  <legend id=legend-right>right</legend>
</fieldset>
<fieldset>
  <legend id=legend-10>10px</legend>
</fieldset>

<script>
 const legends = document.getElementsByTagName('legend');
 const [legendLeft, legendCenter, legendRight, legend10] = legends;

 const expectedLeft = 8 + 10 + 20;
 const expectedCenter = expectedLeft + (500 / 2) - (200 / 2);
 const expectedRight = expectedLeft + 500 - 200;
 const expected10 = expectedLeft +