.container {
  /* Use viewport units for a full-page container */
  height: 100vh;
  width: 100vw;

  /* Turn on Flexbox */
  display: flex;

  /* Center horizontally */
  justify-content: center;

  /* Center vertically */
  align-items: center;
}

.white-square {
  width: 100px;
  height: 100px;
  background-color: white;
  border: 1px solid black;
}