In this detail of the previous image, one can see the blue glass mosaic background with a field of gold stars.
The image of the Lion of St. Mark is seen all over Venice, on flags, decorative items and even clothing.

The mosaic tesserae sparkle here, because the mosaicists set each small glass piece at angles to catch the light.
Mosaics on walls are generally made this way, but those on floors are made so that the glass tesserae are flat to walk on.