Fix: Correct button placement under YouTube player using appendChild

[tarun2684]

This PR updates the button placement logic for ImprovedTube buttons under the YouTube player.

• Ensures buttons are appended after existing elements using appendChild.
• Removes existing .improvedtube-player-button elements to prevent duplicates.
• Improves compatibility across layout variations using updated container selectors.

Fixes alignment issues and improves UI consistency.

[ImprovedTube]

hi and thanks! @tarun2684
are you referring to the bug mentioned at #3021 (comment) ?

instead of editing improvedtubeYoutubeButtonsUnderPlayer you submitted a short extra definition of it?

(Will you finish this or document what's left to do?)
Thanks!

[tarun2684]

Thanks for sharing these detailed logs and observations — this is super helpful!

From the stack trace and behavior you've described (especially the Uncaught TypeError: Cannot read properties of null (reading 'parentElement')), it seems like the YouTube player DOM may not be fully initialized when improvedtubeYoutubeButtonsUnderPlayer() tries to run.
I'll take a closer look at the error lines in appearance.js:505 and functions.js, and see if we can safely add checks for null or delay execution until the elements are available.
Really appreciate your help in tracking this down — I’ll follow up soon with a patch suggestion or a PR.