Certain UI elements can be configured from external sources by providing their public url location. This includes button icons and reaction animation (Firework uses Lottie player).
SVG images will be injected into player DOM so they have access to currentColor variable and are properly colored based on theme. SVG images location has to comply with CORS policy against your origin. Other image types are rendered as background images, can't use theme color and don't require special treatment.
List of supported custom UI assets:
// Generalui_asset_back // Back button asset. Defaults to "<" ui_asset_close // Close button asset. Defaults to "x"ui_asset_next // Next item button asset (video, product image). Defaults to ">"ui_asset_previous // Previous item button asset. Defaults to "<"// Playerui_asset_closed_captions_disabled // CC button asset to indicate disabled stateui_asset_closed_captions_enabled // CC button asset to indicate enabled stateui_asset_fullscreen // Fullscreen button enlarges player to maximal sizeui_asset_menu // More actions menu button asset. Defaults to "3 dots"ui_asset_minimize // Minimize player to PIP.ui_asset_muted // Muted state button asset.ui_asset_unmuted // Unmuted state button asset.ui_asset_pause // Pause button asset.ui_asset_play // Play button asset.// Livestreamui_asset_reaction // Reaction button. Defaults to "Heart"ui_asset_reaction_animation // Reaction button Lottie animation json. Use any lottiefiles.com animation.// Commerceui_asset_shopping_bag // Shopping bag button asset.ui_asset_shopping_cart // Shopping cart button asset.ui_asset_product_tag // Product tag displayed on embed feed carousel thumbnail