<style>
.previous_sibling {
  height: 50px;
}
.float {
  float: left;
  width: 50px;
  height: 50px;
  background: blue;
}
#content {
  overflow: hidden;
  margin-top: -50px;
  width: 50px;
  height: 50px;
  background: green;
}
</style>
PASS if green box shows.
<div class=previous_sibling>
  <div class="float"></div>
</div>
<div style="position:absolute"></div>
<div id="content"></div>

<div class=previous_sibling>
  <div class="float"></div>
</div>
<div style="display: flex"></div>
<div id="content"></div>