<div id="page-wrapper">
  <div class="panel-row">
    test
  </div>
</div>
html,
body {
  margin: 0;
  padding: 0;
}

#page-wrapper {
  min-height: 100vh;
  display: flex;
  background: blue;
}
.panel-row {
  flex: 1 0 0%;
  background: green; /* will cover blue*/
}
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