The background music can be added in the following way:

1. Expand the Page Properties https://cdn.elev.io/file/uploads/Nx6j1ilgYkjKwwUzxKv9Jx2yWyIGUZG4VbEE9W71H30/6An-X6YS10RV2N8TeGGcDFNFvhLiXzxXe7Quj4kbMDI/page-properties-7WM.png panel from the right toolbar.

2. Click the Browse (...) button and select a sound file from the library.

https://cdn.elev.io/file/uploads/Nx6j1ilgYkjKwwUzxKv9Jx2yWyIGUZG4VbEE9W71H30/0cL3ge2f1anKLrUkXL92UwaW3NZusAxKTBTycXg24PE/Ading background music.fw-TWo.png
Note: At this moment we support only MP3, MP4 files.

3. Save the page and your done!