Sheet Styles empowers you to change your background color, font color, and font family while you work on specific tasks. The style can change to a paper or papyrus style, with less contrast. This allows you to work longer hours in sheets. And then when you're done with work you can change back to default Arial font and the white background along with the black font.  

Other styles allow you to change your sheet to "dark mode" where the background is dark and the text is light.