Hi Sibony,
Problem is becuase of styles loaded by RSForms. You used UIKit instead of Boostrap or Fundation everywhere, that's why you see small differences. It's not a Template or SPPB issue. It was a small mistake made by webmaster choices.
Solution:
- In theory by Custom CSS it can be improved (more thinking).
- or in each Form (RsForms) set the same Responsive Layout (in Form Properties tab) as you used on home page "Contactez-nous", then the same styles will be used everywhere.
Now it's your task, I only share "why".