I think this is a good idea, but it seems like you've made the .css file more minimalist than the actual website. I guess there's a distinction to be drawn between making YouTube less appealing to get distracted by, and making the YouTube experience nicer by reducing distraction and noise. If you're going for the latter, here are a few tweaks I would suggest:

* Pick a more aesthetically pleasing than default font, ditch the blue default link colors.

* Normalize the thumbnail size.

* Consider normalizing the video titles to all lowercase. It's still possible to search for something and see all caps everywhere which feels very noisy to my brain.

* Consider leaving the descriptions off altogether

But still, very cool idea!