What are the differences between these IFR Low Altitude Chart Navaid Symbols?
The shadow in the NAVAID box indicates that the NAVAID and FSS have the same name, as in your top image. If they are different, the FSS name is given in brackets below the NAVAID box, as in your bottom image. If the FSS is not available, a thin line box is used for NAVAID (without brackets at the bottom), as in the middle figure. 

FAA Aeronautical Chart User's guide should help you understand it better.



Image from FAA Aeronautical Chart User's guide