Twine2 is a great tool for beginners to make games, but there aren't customization options out of the box, and the way to use CSS is not well documented. This template is a well-commented basic reset that allows you to make your game look unique without knowing too much about CSS.
Cut and paste the CSS template into Twine2's CSS Section
Modify fonts and colors to your liking following the instructions in the CSS, or just use as-is, an extremely readable basic template.
Right now, there is only a template for customizing Harlowe games. I'm working on a template for SugarCube, but until then, use the official basic template, called Bleached: http://www.motoslave.net/sugarcube/2/
(This means there aren't any meaningful restrictions on how you can use it, you just can't sue me over it.)