BetterYTM-Mirror/assets/style/fixPlayerPageTheming.css

/* This file should only be loaded if the ThemeSong extension is ***NOT*** installed */

:root #side-panel ytmusic-player-queue-item[play-button-state="loading"],
:root #side-panel ytmusic-player-queue-item[play-button-state="playing"],
:root #side-panel ytmusic-player-queue-item[play-button-state="paused"] {
  background-color: #1d1d1d !important;
}

:root
  #side-panel
  ytmusic-player-queue-item[play-button-state="loading"]
  .bytm-queue-btn-container,
:root
  #side-panel
  ytmusic-player-queue-item[play-button-state="playing"]
  .bytm-queue-btn-container,
:root
  #side-panel
  ytmusic-player-queue-item[play-button-state="paused"]
  .bytm-queue-btn-container {
  background: linear-gradient(90deg, rgba(0, 0, 0, 0) 0%, #030303 15%);
}

:root
  #side-panel
  ytmusic-player-queue-item[selected][play-button-state="loading"]
  .bytm-queue-btn-container,
:root
  #side-panel
  ytmusic-player-queue-item[selected][play-button-state="playing"]
  .bytm-queue-btn-container,
:root
  #side-panel
  ytmusic-player-queue-item[selected][play-button-state="paused"]
  .bytm-queue-btn-container {
  background: linear-gradient(90deg, rgba(0, 0, 0, 0) 0%, #1d1d1d 15%);
}

:root
  #side-panel
  ytmusic-player-queue-item[selected]
  .bytm-queue-btn-container {
  background: linear-gradient(90deg, rgba(0, 0, 0, 0) 0%, #1d1d1d 15%);
}