It should be one line of code.
This part of your code is correct
document.getElementById(`song-${userData?.currentSong?.id}`);
and this part
const songToHighlight =
Now combine the two into one line of code.
I’ve edited your code for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.
You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.
See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (').