Form fields are stretching full-width and split into 2 lines

My form's fields are stretching to the full width of the screen, putting First Name / Last Name and Area Code / Phone Number on separate lines from each other: 

How do I fix this?

I inspected your account but unfortunately I could not locate the form, as you have several forms. Please let us know the form's url and the website's url (in case it's embed) so we can investigate further this situation.

Thank you