The mode property of the background tells the mod how it is supposed to fit the background image in the minecraft window.
- fill : Will keep the aspect ratio of the image and will make sure that the image covers the whole screen, to do that it will cut off parts of the image if it is not possible otherwise.
- stretch : Will resize the image so that it fits the whole window, it does not keep the aspect ratio of the image.
- center : Will simply place the image in the center of the screen, if it's too large it will be cut off, if it's to small there will be black borders.
- tile : Will fill the window with a grid of the specified image, this is useful for backgrounds that display a certain texture.