Modern website

[Andrew Z]

I realize the following has little todo with python per se. But i hope to
get a guidance on how these types of tasks are done nowadays.

The task:
Ive been asked to create  an integration process. That is a few webpages
with questioneer with the submission to a "mother" company using its API .
Ideally this process will be used by a few 3rd party "child" companies -
they would just point a link from their site to mine. Prospective users
will fill out the pages and "mother company" will create accounts
associated with the referal "child" company.

The problem:
  how do i create a modern , slick  website. I also see , that each of
"child" would want to extend the look and feel of their site onto this
process. So, my process should have at least a few templates i can offer ,
that would match their site...
Im not too excited to use weebly or squarespace - id rather host everything
myself.