/* The root container wrapping nav-rail + panels */
:host, .app-root, body {   /* whichever is the parent */
  display: flex;
  flex-direction: row;
  height: 100vh;
  overflow: hidden;
}

.nav-rail {
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
}

.panels {
  display: flex;
  flex-direction: row;
  flex: 1;
  overflow: hidden;
}

.app-root {          /* or :host, body, whatever your root element is */
  display: flex;
  flex-direction: row;
  height: 100vh;
  overflow: hidden;
}