Basically you're creating an iframe (explanation of that here) that opens up youtube inside of your profile. In mine I have the height/width of the frame set to 0 so it's invisible, and I have it set to autoplay so it starts right away. Other people have the height/width set so it's like a box you can actually see in their about-me, and in it is just the youtube video you can play/pause by clicking on it.
The embed is the link for the video. You don't want the link to be to the video itself because then that'll open up comments, likes, dislikes, recommended, etc. and you just want the video.
so you'll put this in your about-me section (not in your CSS! because this is content to go in your page, not styling for it):
<iframe width="0" height="0" src="https://www.youtube.com/embed/CODEGOESHERE//?&;amp;;autoplay=1&;loop=99&;controls=1" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen="" loading="lazy">
</iframe>
basically all you would change is the width="0" height="0" (if you don't want your music to be invisible, like on my profile) and then the CODEGOESHERE part. In the CODEGOESHERE part, you'll open up the youtube video with the music you want to play, and the link will look like this:
https://www.youtube.com/watch?v=Xqci3BMjpJc
you'll copy the part after /watch?v= and that is what you'll paste in the CODEGOESHERE bit. So then you'll get this:
https://www.youtube.com/embed/Xqci3BMjpJc//?&;amp;;autoplay=1&;loop=99&;controls=1
and that's the link that will play your music for you :)