Custom subscribe button on landing page

[Olshansk]

Goal

My goal is to add a "Subscribe" button on the front page linking to my email provider of choice.

What I've looked into

1. Override index.html - I want to customize it rather than override it
2. Add customCSS - I'll need once I figure out (1).

Question

I realize this isn't hard, but I also wanted to ask if there are docs/instructions/examples of how others have done this in the past before I jump into the 🐰🕳️?

Opening up an issue because I couldn't find it myself.