1

    1. main {
    2.  position: absolute;
    3.  top: 50%;
    4.  left: 50%;
    5.  transform: translate(-50%, -50%);
    6. }

    2

    1. main {
    2.  width: 18em;
    3.  padding: 1em 1.5em;
    4.  margin: 50vh auto 0;
    5.  transform: translateY(-50%);
    6. }

    3

    1. body {
    2.  display: flex;
    3.  min-height: 100vh;
    4.  margin: 0;
    5. }
    6. main {
    7.  margin: auto;
    8. }

    4

    1. main {
    2.  display: flex;
    3.  align-items: center;
    4.  justify-content: center;
    5.  width: 18em;
    6.  height: 10em;
    7. }