html,

body,
html {
  margin: 0;
  background-color: rgb(100, 113, 99);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 100%;
  height: 100%;
  background-repeat: no-repeat;
  background-size: cover;
  background-position: center;
}

main {
  display: flex;
  align-items: center;
  justify-content: center;
}