Time Tracking Challenge using Grid and Json Data

I struggled with designing the color icon tab that was underneath each section. My approach was to create to image with position: absolute inside of a position: relative container, but once I started adding in z-index values the stacking context got a little confusing to me so I'm curious how other people designed that portion. Also I have never worked with incorporating json data before so I'm interested in how other people approached that as my method feels a little clumsy to me and I think it could probably be handled more succinctly. Any feedback is greatly appreciated!