html, body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  background: #232323;
}
main {
height: 100%;
display: flex;
align-items: center;
justify-content: center;
}
#center {
  flex: none;
  max-width: 99%;
  max-height: 99%;
}