html,
body {
  height: 100%;
}

body {
  overflow: hidden;
  display: flex;
  justify-content: space-evenly;
  align-items: center;
}

.circle {
  width: 15vw;
  height: 15vw;
  border-radius: 50%;
  background: red;
}

.circle:nth-child(odd) {
  background-color: blue;
}