Missing highlight for NotifyBackground

[vihu]

It seems like NotifyBackground highlight is unimplemented.

Error:

Highlight group 'NotifyBackground' has no background highlight
Please provide an RGB hex value or highlight group with a background value for 'background_colour' option.
This is the colour that will be used for 100% transparency.

require("notify").setup({
  background_colour = "#000000",
})

Defaulting to #000000