ohif-viewer/platform/viewer/src/connectedComponents/ViewerMain.css

#viewer {
  height: calc(100% - var(--top-bar-height));
}

#viewer > .loadingTextDiv {
  color: var(--text-secondary-color);
  font-size: 30px;
  height: 100%;
  line-height: calc(100% - var(--top-bar-height));
}

.ViewerMain {
  width: 100%;
  height: 100%;
  transition: all 0.3s ease;
}

.ViewerMain > div {
  width: 100%;
  height: 100%;
}