matrix-dimension/web/app/widget-wrappers/jitsi/jitsi.component.scss

// component styles are encapsulated and only applied to their components
#jitsiContainer {
  position: fixed;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  display: none;
}

.join-conference-wrapper {
  display: table;
  position: absolute;
  height: 100%;
  width: 100%;
  background-color: #fff;
}

.join-conference-boat {
  display: table-cell;
  vertical-align: middle;
}

.join-conference-prompt {
  margin-left: auto;
  margin-right: auto;
  width: 90%;
  text-align: center;
}