I don’t work for Gravity Forms, but at the heart of the new Orbital theme is CSS variables. Where CSS variables shine is creating “themes”, and I suspect “Orbital” is just the first of many themes that will become available in the future (don’t hold me to that though 
).
To give you a practical example, take a look at this recent forum post: Styling the submit button
The first reply uses the old way of styling a form, which requires tracking down all required selectors and then overriding them. The second reply (mine) uses three CSS variables to apply a new “theme” to the form. Gravity Forms documentation could certainly be improved in this area, but I know which method I prefer.