Content is sourced OK but design not updated

I finally managed to install ghost for free on the jamstack. but I have one question:
my content is correctly sourced from my Heroku Ghost install and netlify deploys correctly. but the design of the blog isn’t updated. how come? I’m stuck with casper and the design of the Gatsby starter project. >>

Based on my understanding. You have to work on Gatsby Design files.

Because Ghost is running as headless CMS it can only update content of blog. Not design.