Look at FAQ on this page. Under ‘Design’ see ‘Is possible modify any of predefines templates included with the plugin’.
“The plugin includes multiple templates that can be assigned to the Forms to display a predefined design: Default template, Letter template, Professional, Natural, Elegant, Decorative and Clean Design.
Each template is stored in its own directory, in the “templates” folder ( “/wp-content/plugins/calculated-fields-form/templates”). Basically the templates are formed by a CSS file ( style.css ). If you want change the appearance of a predefined template, you simply should modify the style.css file corresponding to the template. The directories of each template are:
Letter Template: templates/01 directory.
Professional Template: templates/02 directory.
Natural Template: templates/03 directory.
Elegant Template: templates/04 directory.
Decorative Template: templates/05 directory.
Clean Design Template: templates/06 directory.”