<div class="in">1in</div>
<div class="px">96px</div>

BODY {
  min-height: 100vh;
}

BODY, DIV {
  display: flex;
  align-items: center;
  justify-content: center;
}

.in {
  width: 1in;
  height: 96px;
  margin-right: 3rem;
  background: pink;
}

.px {
  width: 96px;
  height: 96px;
  background: palegreen;
}