Make an overlay, copy its link, add it to OBS as a Browser Source (1920 × 1080).
Good to know
Your overlays are saved in this browser. Use Back up now and then, and Restore on another computer.
The OBS link holds the whole overlay, so OBS doesn't need this dashboard open. Change an overlay → copy its link again → paste it into OBS.
Using your own picture or video? Put the file in the assets folder, redeploy the folder in Cloudflare, then type assets/your-file.png as the background. A full web address to an image works too.
In OBS, tick Refresh browser when scene becomes active so countdowns restart.