html – SharePoint Custom Landing Page

I have created a very simple HTML single page which I want to use as a “Landing Page”. Is it possible to replace the whole page with the HTML page? I’ve tried a web part page, and a wiki page and once it is in a web part, that is all it stays in leaves so much random white space, etc. My custom navbar, also covers the SharePoint settings and top ribbon so I am unable to even edit the page anymore because of the way it is.

Here is my JSFiddle: in my version everything is centered, not sure why the heading text is not centered: