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<span id="trigger-office"></span>
<span class="spacer"></span>

<div class="viewport"></div>
<!-- viewport -->

*,
*:before,
*:after {
  box-sizing: border-box;
}

.spacer {
  width: 100%;
  height: 400vh;
  display: block;
}

.viewport {
  width: 100vw;
  height: 100vh;
  display: block;
  position: fixed;
  top: 0;
  left: 0;
}