SVG Background Source

Is there a way to use svg as background in a container?

You should just be able to add it as the image option in a Container Plus stack as with any other image.

An alternative approach is to use the likes of Grid Plus Pro instead of the container stack and layer 2 grid items (i.e. both in col 1 and row 1) and put an SVG stack in the rear one (setting its max-width to e.g. 9999px).