metamask-extension/ui/app/components/network-display/index.scss

.network-display {
  &__container {
    display: flex;
    align-items: center;
    justify-content: flex-start;
    background-color: lighten(rgb(125, 128, 130), 45%);
    padding: 0 10px;
    border-radius: 4px;
    height: 25px;

    &--mainnet {
      background-color: lighten($blue-lagoon, 68%);
    }

    &--ropsten {
      background-color: lighten($crimson, 45%);
    }

    &--kovan {
      background-color: lighten($purple, 65%);
    }

    &--rinkeby {
      background-color: lighten($tulip-tree, 35%);
    }
  }

  &__name {
    font-size: .75rem;
    padding-left: 5px;
  }

  &__icon {
    height: 10px;
    width: 10px;
    border-radius: 10px;

    &--mainnet {
      background-color: $blue-lagoon;
    }

    &--ropsten {
      background-color: $crimson;
    }

    &--kovan {
      background-color: $purple;
    }

    &--rinkeby {
      background-color: $tulip-tree;
    }
  }
}