are you able to make the "spacehey blue" an image?

ive been on spacehey for a while but never really coded my own stuff, ive taken my past experiences coding very little things (like little mistakes or changing phrases) and im attempting to code an image as the background the big blue banner of the spacehey profile, but it just ends up as a color only. i figured it would be like coding the background? but im not sure, ive never really coded things myself, only edited other's.

i know you can edit the color of it, but are you able to add a background image to it?