What if, post battle of Hogwarts say around now, students sorted into Slytherin (more often muggle borns ) would take fairy or Christmas lights and hang them around their beds to make it cozier. Most not being accustomed to the seriousness of the living space, and tradition no longer making the horrible vibe normal. They would also add gauzy drapes, posters, throw rugs and cushions, candles, quilts and little things to make their bed space brighter. This caught on quickly with the other Slytherins because who wants to live in a scary dungeon, and soon it became a contest seeing who could have the warmest, comfiest, and coolest bed. Slytherin was no longer scary on the inside, but of course they didn’t tell the other houses that because no one wanted to loose the mysterious factor.
Me- YESSSS I am behind this one hundred percent. You can’t tell me those pampered Slytherin don’t make everything as comfortable as possible for themselves. I’m pretty sure even before the battle not everything was as severe and intimidating as their common room. Slytherins like their appearances;) headcanon accepted, definitely. Thanks for the submission!