matrix-public-archive/public/styles/styles.css

/* Based on .SessionView from Hydrogen */
.ArchiveView {
  /* this takes into account whether or not the url bar is hidden on mobile
  (have tested Firefox Android and Safari on iOS),
  see https://developers.google.com/web/updates/2016/12/url-bar-resizing */
  position: fixed;
  width: 100%;
  height: 100%;
  display: grid;
  grid-template:
    'status status' auto
    'middle right' 1fr /
    1fr 300px;
  min-height: 0;
  min-width: 0;
}