Help: Product Landing Page - Margin/Padding Issues

Working on the Product Landing Page project and need some help.
[Product Landing Page]
Something is sabotaging margins and padding. I mean, obviously I’m what’s sabotaging it, but I don’t know what I’m doing ¯_(ツ)_/¯

The problem manifests on the right side of the page, and it is very apparent when the screen width is narrow.

I thought it was a flex issue, since I had some problems putting a margin on the right side of the form and .pack is expanding outside of it’s container. But the h1 also has a problem and is putting text off the page when narrow.

Of note: I have a CSS reset, but removing it doesn’t resolve anything. Appreciate the help!

Getting somewhere. Resolved content going off page and out of container by setting all elements to:

* {
	box-sizing: border-box;

Problem appears to be with width=100% calculations and the parent/inheritance rules of the content-box model.