This simplified mural has bubbles coming from different points of the room and help provide the illusion that this room is underwater. The bubbles are painted in such a way that they appear to be interacting with the letters on the wall.
There are many different levels of detail in a mural. Higher detail usually has more color, tones, lines and components. Low level detail is usually fewer colors, and less variety. Depending on what is being painted, the level of detail may go up or down for things that require more attention.