The display is a flame graph corresponding to statistical profiling of the workers. The whole CPU effort is the x-axis of the set of colourful blocks, and as you travel upwards, you are moving deeper in the call stack, e.g.,
You can get information about the function corresponding to each block by mousing over.
Note that some function call stacks can be very deep, e.g., pandas processing.
You can also select which submitted function you are looking at the profile for (top), or select from the overall CPU utilisation timeline (bottom).