Link from Express store to existing home page

[stairsolutions]

I have finished building my Express store and want to link to it from a page in my existing website. That seems easy. But how can I link back to my existing website from the Express store. I would like to make it look seamless as if it is all one website probably by using the Home link on my Express front page to link back to my existing website home page but this doesn't seem possible.
Has anyone else built their Express store into their existing website?