It looks like YouTube is testing new design with Material Design. I got two google chrome accounts, and one of them uses the new youtube layout. Opening YouTube in incognito shows the old layout.
If you click the exclamation mark button, a popup opens where you can report bugs or features, it also takes a screenshot. Clicking on the exit button, a popup opens with different choices and it'll take you back to the old layout.
Anyone else got the new design?