Gravity Forms comes with very deep selectors that are hard to override. If you disable the css output then you get nothing at all.
This comes to remedy that by giving you some simple styling that can easily be overriden. The styles are simplistic and give you nice forms that look good on desktop and mobile.
To use just disbale the css output for gravity forms via gravityforms>settings Then add the css or scss file to your theme.
You can use the class separate-fields on a complex field such as first name and last name fields. This will separate the fields out onto separate lines.