Depends on your form’s structure, and the styles defined into the theme active on your website. For example, assuming you have defined the DIV field to distribute the fields in two columns, you can enter the following style definition into the “Customize Form Design” attribute in the “Form Settings” tab:
Through this attribute you assign a class name to the fields, but the styles must be defined through the “Customize Form Design” attribute in the “Form Settings” tab. You cannot enter the CSS rules directly through the “Add CSS Layout Keywords” attributes.