ol-layerswitcher/examples/scroll.css

/* Set a small height to demonstrate the layer switcher scrolling */
#map {
  max-height: 300px;
}

/* Fixed max-height for IE11 to support scrolling, due to incomplete support for flexbox */
@media all and (-ms-high-contrast: none), (-ms-high-contrast: active) {
  .layer-switcher.shown {
    max-height: 170px;
  }
}