According to https://material.google.com/material-design/environment.html#environment-light-shadow , there are key light and ambient light. What confuses me is the location of the light source.
Besides, soft shadow is shown in material design, so the the key light should be area light instead of point light. Then, what is the size of the area light?
According to this question https://graphicdesign.stackexchange.com/questions/80644/where-are-the-light-sources-located-in-material-design the key light is