@lonelyplanet/dotcom-core/src/components/_backpack/overlay/styles.css

This package is meant to house some of our more common UI and shared libs across dotcom applications.

.overlay {
  background-color: rgba(0, 0, 0, 0.3);
  bottom: 0;
  height: 100vh;
  left: 0;
  position: fixed;
  right: 0;
  top: 0;
  width: 100%;
  z-index: map(zIndex, overlay);
}