How to style front end submission form

Hi,

The plugin outputs the HTML with custom CSS classes. You can filter to the output of each field to add Bootstrap classes if you want, but that will be a huge work. See the filters here:

https://docs.metabox.io/filters/

I'd suggest you write some custom CSS for the fields. Please inspect the fields' output and add CSS for them. The plugin already output some basic CSS to make them work, and you only have to write CSS to make them fit your design.