Submit Button to Match the Theme

G’day

Does anyone know the code I would use to place a submit button in a post, that will still maintain the same theme settings as regular buttons.
For example there is a button as part of the jet pack plugin that allows users to subscribe to the blog. It does a custom function but it matches the theme of all the other buttons.

I basically would like a submit button that will look like the rest of the buttons which I can then link to the registration page.

https://www.theflamencogypsy.com/category/resources/

Cheers
Fisch