*{ box-sizing: border-box;}

#outer{
  width: 70vmin;
  height: 70vmin;
  background-color: darkslategray;
  padding: 15vmin 11vmin 15vmin 11vmin;
  margin: 0 auto;
}

#secondring{
  height: 50vmin;
  background-color: goldenrod;
  padding: 12vmin 7vmin 15vmin 7vmin;
}

#innersquare{
  height: 30vmin;
  background-color: red;
  padding: 5vmin;
}