I got the same requirement and I have done some customization for this.
Step 1: Go to core database and under this location (/sitecore/client/Applications/FormsBuilder/Components/Layouts/PropertyGridForm/PageSettings/Settings) create a new control by copying DropDownList and name it CascadeDropDownList. Under this new control, add some text box parameters ...
To start using custom styles and scripts in your forms:
In the Content Editor, navigate to sitecore/Forms, click the form that you want to add a script or style to and, in the Scripts or Styles field, add the name of your custom script or style file.
Add your custom style or script file to one of the following folders:
Scripts : /sitecore modules/Web/...
You can below link for Sitecore Form styling - https://doc.sitecore.com/developers/90/sitecore-experience-manager/en/add-styles-and-scripts-to-sitecore-forms.html
Sitecore Forms uses css and script files located in: <siteroot>/sitecore modules/Web/ExperienceForms
So for css you can go to path - <siteroot>/sitecore modules/Web/ExperienceForms/css