You'll notice
Composer sidebar background is now always shown when a sidebar is present, removing the fill toggle
What
The layout component that renders the transcript, sidebar, and composer area no longer has a way to turn off the sidebar's background fill. Whenever the sidebar has any width, its composerSidebarBackground color is now always applied.
Why
The optional transparent/inherited sidebar look is no longer available; the sidebar's filled background is now the only behavior.