message: Use better z-indexing for AppMediaItemBackdrop
diff: .media-item-backdrop
  + position: relative
  + z-index: 0
  display: flex
  overflow: hidden
  width: 100%
  height: 100%
  - position: relative
  -
  - > *
  - position: relative
  .-color
  position: absolute
  + z-index: -1
  top: 1px
  right: 1px
  bottom: 1px
  