The guideline for designing icons used to be that you should be able to draw it in the sand with a stick. Icons devoid of details and focusing on the bare elements to convey its associated function were standard, for this graphical approach would resonate with the largest amount of users.
However, with the popularity and growth of the smartphone and mobile device market, icons design for apps started taking on more realistic features. The focus of the app icons was not to resonate with the largest number of users, but rather to act as an identifier for the specific application. As a result, consumers have become used to seeing 2-dimensional icons with bolder colors and added detail, which can add to the overall user experience.