html, body {
    height: 100%;
}

html {
    display: table;
    margin: auto;
}

#dialog {
  position: absolute;
  z-index: 9;
  background: gray;
  width: 15rem;
  height: 20rem;
  padding: 5px;
  overflow: scroll;
}

#dialogheader {
  padding: 1rem;
  cursor: move;
  z-index: 10;
  text-align: end;
  background-color: #2196F3;
  color: #fff;
}