Theme Settings provides global colour and font settings of the form (which can be customized further for different form elements in Typography)
Typography allows you to change question title, description text, input box and textbox elements in terms of font, height, spacing, colours and more.
UI elements is detailed section for the form & background design as well as various design elements of the form, incl. question fields, customization of radio, select buttons and visual image/icon questions.
Step navigation provides you with all the options to change the Back, Continue and Submit button settings, for example Call-to-action text, button sizing and behaviour on hover and submit.
If you like to look deeper into designing forms, here is a Form Design Video Tutorial