The HL15 comes with separate rack ears that screw onto each side extending the face to cover the rails. The reason for this design is that the HL15 can also be used in a tower orientation by/under a desk, which wouldn’t work very well with a faceplate with permanent rack ears.
https://forum.45homelab.com/t/deployed-my-hl15/751/11
The ears will match the case color you order (black or white).
Lots of equipment comes with optional ears rather than fixed ones so it can be used in and out of a rack.