html, body {
  height: 100%;
}

/* Make is-hidden always win */
.is-hidden {
  display: none !important;
}

.box-small {
  max-width: 28rem; /* ~448px */
  margin-left: auto;
  margin-right: auto;
}

.box-medium {
  max-width: 40rem;
  margin-left: auto;
  margin-right: auto;
}