Hi ryojii ,
Are you using "Form hosting" for this one?
If yes, then there are two ways to implement this
1. Host it as a script
choosing host as a script option, marketing form will uptake styles of the hosting website, the form becomes a part of the website layout, also the form will track clicks made on the website.
2. Host it as an iFrame
choosing host as an iframe option, marketing form will stay isolated from the layout of the website, styles of the form will be sandboxed, also the form will not be tracking clicks made on the website.
based on the selection you might have to make necessary adjustment to either the form in dynamics or where you are hosting it.
If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Hari