Hi Max,
I use this method. The background has become transparent. But my website don’t play any sound now and the auto-play function also not working. Do you have any ideas why it’s happening?
Hello there, @Maxine_Lillian and welcome to the Community 
Both issues occur because of the iframes used on the Canva platform.
Unfortunately, there is nothing can be done with the autoplay feature. However, to make the tracks play on click please upload them as files instead of adding links. This should help you resolve the issue.
Check it out and let me know if it helped 
Thank you for your advice. I have changed the songs into sound track file instead of Youtube link and it works now.
No sweat!
If any other questions come up, I’ll be happy to help 