Contained DIV

by resistdesign

HTML

<div>

</div>

CSS

html, body {
  margin: 0;
  padding: 0;
  width: 100vw;
  height: 100vh;
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: center;
}

div {
  background-color: red;
  width: 100vh;
  height: 100vw;
  max-width: 100vw;
  max-height: 100vh;
}