So I was watching YouTube in my Chrome browser on my Mac, and I accidentally leaned on the left edge of my keyboard as I was pushing my chair away from the desk.
Now my YouTube video player window is "too small" for the video it contains. The right edge of the video is cut off when I watch a video in "normal" mode, and the bottom edge is cut off when the video is in "full screen" mode.
Worse -- this setting seems to be tied to my Google Chrome browser and the account settings! I deleted and re-installed Chrome on my Mac and the problem still exists. I tried YouTube on my Windows PC, in a Chrome browser that's signed into the same account my Chrome browser is on my Mac, and the problem is there too! Just to verify it's not tied to my YouTube account, I tried it in Safari, signed into my YouTube account, and the problem is NOT there.
So clearly I hit some kind of keyboard shortcut that "zoomed" in just the video-player window inside Chrome? And saved it to my Google account, so all my Chrome browsers are now broken on YouTube?!