dungeon-master-viewport.html

<div class="viewport">
  <div class="background"></div>
  <div class="ll3 far-left-wall"></div>
  <div class="rr3 far-right-wall"></div>
  <div class="l3 left-wall"></div>
  <div class="r3 right-wall"></div>
  <div class="fl3 front-wall front-wall-farther"></div>
  <div class="ff3 front-wall front-wall-farther"></div>
  <div class="fr3 front-wall front-wall-farther"></div>
  <div class="l2 left-wall"></div>
  <div class="r2 right-wall"></div>
  <div class="fl2 front-wall front-wall-far"></div>
  <div class="ff2 front-wall front-wall-far"></div>
  <div class="fr2 front-wall front-wall-far"></div>
  <div class="l1 left-wall"></div>
  <div class="r1 right-wall"></div>
  <div class="fl1 front-wall front-wall-near"></div>
  <div class="ff1 front-wall front-wall-near"></div>
  <div class="fr1 front-wall front-wall-near"></div>
  <div class="l0 left-wall"></div>
  <div class="r0 right-wall"></div>
</div>