Can a shader add transparency to scene borders? (VR UI)

Hi, I'm working in this tridimensional spatial/diegetic UI:

The panels in the screenshot should be opaque in the middle area and loose transparency as they get closer to the borders (green rectangles). Can I gradually increase transparency at borders using a shader? Sorry if this is a really bad question... I'm not experienced with shaders. Do you have a better idea for implementing it?

This panels will scroll vertically and horizontally, and right now my only other idea is calculating transparency from the panel's actual transform position. I don't like this idea :(