How to Use Surface Elevation to Elevate Your Interface
The right way to use drop shadows
All user interfaces are a collection of surfaces. You have the background, foreground, and the elements that float on top. To show users what screen elements are active, you have to use surface elevation.
Some components that need elevation are toasts, cards, and menus. When you fail to use elevation, these components can look like they are part of the background or content. As a result, users can overlook them and fail to interact with them promptly.