For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
would it be in this section ???You can do what you want with css.
thanks for the info.No, this is CSS is for list.
Inspect the element id/class with browser and add the bottom border as CSS in your form template's custom.css or custom_css.php file.