Play Youtube in background

Although YouTube is all about video streaming, there is plenty of content on there that doesn’t actually require you to watch any footage, such as music and pod casts. Unfortunately, you can’t minimize the YouTube app without pausing the current video
Google’s Chrome browser OR  google android browser which official comes to your phone that allows you to leave videos playing in the background.




Next up, you must pause the video and then switch to another tab or app. The volume notification will remain in place, hit play, and you can continue to listen to the video in the background. It’s that simple, but the video be can also guide you through the steps. You can switch in and out of apps and the video will still play, and playback can even be controlled from the lock-screen.

also you try switching desktop mode still you didn't get it watch the video  

FOR the RICH DUDES BUY 

YouTube Red is a paid membership, available in certain countries, that gives you an amplified video and music experience across YouTube, YouTube Music, YouTube Gaming, and YouTube Kids. Learn more about the benefits of a YouTube Red membership below. 

Ad-free videos

Save offline

Background play

YouTube Red Originals

Free Google Play Music subscription

 A few notes: YouTube Red benefits are not compatible with rented/purchased movies and TV shows, or paid channel subscriptions. Not all benefits may be available on third-party sites that embed YouTube content. Finally, your YouTube Red membership also helps to support YouTube creators.

Start your YouTube Red membership

ANDROID IPHONE & IPAD

Become a YouTube Red member to access benefits on YouTube, YouTube Music, YouTube Gaming, and YouTube Kids. 

Note: To purchase a YouTube Red membership, you'll need to make sure your home address in Google Payments matches the country where you're trying to purchase YouTube Red. Visit the Google Payments Help Center for more information on how to edit your home address.

http://youtube.com/manage_red

If your rooted and poor hacker things can be done more Romantic 

 https://android.gadgethacks.com/how-to/enable-youtube-background-playback-for-free-android-nougat-0175606/