The editor uses Equirectangular Panoramic Images for the background element.
The supported file formats for the Equirectangular Images are: jpg & png
Equirectangular Images have an aspect-ratio of 2:1 and the recommended resolution for the same is 4096 x 2048.
The file size of the Equirectangular Image also affects the load time of a scene in the experience you create. Hence, the recommended file size for an Equirectangular Image for faster loading time is 1MB.