Build your overlay

Set it up here, then paste the link into a Browser source in OBS. The preview updates as you change things; the checkerboard is what your stream shows through.

Channels
A channel name will not work here. On the live Rumble stream, click the popout chat button above the chat and copy that window's URL. The id changes each time the streamer goes live.
Text
1.4x
Usernames keep their platform colours.
Background
0%
0% is fully transparent, which is what most streams want.
0%
Shades individual messages instead of the whole panel.
Behaviour
20
Draws a coloured panel around them. Untick to show every message plainly. Lets you position and style the overlay in OBS before going live. Remember to untick it and copy the link again.
Never
Useful when two channels on the same platform share the feed.
Preview — sample messages
  1. In OBS, add a Browser source.
  2. Paste this link into the URL field.
  3. Set width and height to match your canvas, usually 1920 by 1080.
  4. Leave the custom CSS box as it is and click OK.