body {
  width: 100vw;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

body::before,
body::after {
  display: inline-flex;
  width: 10vh;
  height: 10vh;
  margin: 2vh;
  border: 2px solid blue;
  border-radius: 5px;
}

body::before {
  content: linear-gradient(to right, #f36, #90f);
}

body::after {
  content: "";
  background: linear-gradient(to right, #f36, #90f);
}