Why does it feel good to place the inside of my elbow on my closed eye lids?

They get a break from the screen time. An airplane eye mask, or simply reading a book will have the same inner elbow effect.

You are giving yourself a hug, it’s like having a weighted blanket. Artificial confinement (like swaddling for babies) is comforting.

I use my knees to get the same effect. Something about the gentle pressure. In fact, when my knees hurt, it feels good when I use them to press on my eyes.

Yes, in addition to resting the eyes, you also give your nervous system some soothing unusual stimulus to itself by touching different parts of your own body together. Touching the two sides of your nervous system to each other crosses the hemisphere organization of your nervous system and gives it feedback to/from the halves that are usually separate.

The eyes also are unusual in that each eye is connected to both sides of the nervous system while the arms are only connected to the opposite brain hemisphere… so the eyes are an interesting (to your nervous system) place for your body to touch.

Also people just use their eyes an awful lot, and people who stare at computers a lot tend to also mainly use them only in one specific way. Shifting that up and giving them a break helps them not get worn out.

I find total darkness makes a great difference for sleeping and relaxing. If I don’t have anything else to put over my eyes, I use my arm.