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
The channel name from the Rumble URL, like the other platforms. Pasting a rumble.com/chat/popup/... link also works, but that id changes each time the streamer goes live, so the name is better.
Text
1.4x
Usernames keep their platform colours.
Off
A solid edge around every letter, for bright or busy scenes. Moves in quarter-pixel steps; most text sizes look right between 1 and 2, very large text can take 3 or 4.
Standard
Left packs messages tighter, right spreads them out. With row backgrounds on, extra space appears between the boxes.
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
Names separated by commas. Overlay only: the app still shows them, so mods see everything.
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.