An optional wallpaper behind the messages.
Added
VIEWER_CHAT_BACKGROUNDputs a picture behind the conversation, the way the apps let you set a chat background. Name a file the viewer serves from/staticand mount it into the container; leave it unset and the viewer looks exactly as it does today. While it is on, the message bubbles turn opaque, because the themes draw them translucent over a flat colour and a photo behind running text is not readable, and the image is tinted with the palette's own background colour, so one picture works under a light and a dark theme instead of only one of them. Contributed by @WalterLederer in #432.
Note
The file name is validated as a bare name, so it cannot address anything outside the static directory or add declarations to the stylesheet it is baked into. A name that does not resolve simply leaves the pane plain.
📋 Full changelog: docs/CHANGELOG.md