A post on r/google offers step-by-step instructions for accessing YouTube's new "dark mode", which simply turns the background black and is suggested for a more enjoyable nighttime viewing experience.
To enable dark mode, open the console while you're visiting YouTube and paste the following: document.cookie="VISITOR_INFO1_LIVE=fPQ4jCL6EiE".
YouTube has reportedly introduced a secret dark mode, which can be activated in Chrome relatively easily by making a few changes to your Chrome browser.
Google has been flirting with a "Dark Mode" in Android for a little while now, but it looks like YouTube is taking that experience to the web. Select this option and toggle the switch to enable the turn down the lights - activate the mode.
Open the Chrome developer tools tab.
Close the developer tools sidebar and refresh the YouTube page.
Click the main settings menu in the top right and find the "Dark Mode" section.
If you're anything like me then when you get into bed at night one of the first things you do is pop open a new tab and load up YouTube like some freakish insomniac vampire who needs videos about dogs to survive.