Hey Lisa,
I will go over your questions in the same order:
1). It is generally not recommended to use an image with important information content as a website background image, since on various devices the image will render differently depending on the screen size and aspect ratio (and today there are dozens of possible ones, from 2560×1440 to 320×480 pixels, and everything in-between. Having said that, I should mention that in Kabuki, you are in fact able to control whether the image will be fitted to cover the entire screen (“cover”) or fitted to remain entirely inside the screen area (“contain”), in which case there will most probably be empty spaces either on top and bottom or on the sides of the image, depending on the screen aspect ratio. You can try the “Always fit” setting in the “Size and position” tab of the “Appearance -> Background Settings” admin menu.
2). To force the background image to fit the top left corner of the screen, you can try turning off the “Center the background vertically” and “Center the background horizontally” settings in the “Size and position” tab of the “Appearance -> Background Settings” admin menu.
Sincerely,
Andrii / Satori Studio