Stick content to the left of the page in twenty fourteen (sidebar is disabled)?

I’m using the Fourteen Extended plugin to remove the sidebar; now I’d like to have the content stick to the left, rather than hang out a couple hundred pixels from the left

I found this in the stylesheet on line 4133:

.full-width .archive-header,
	.full-width .comments-area,
	.full-width .image-navigation,
	.full-width .page-header,
	.full-width .page-content,
	.full-width .post-navigation,
	.full-width .site-content .entry-header,
	.full-width .site-content .entry-content,
	.full-width .site-content .entry-summary,
	.full-width .site-content footer.entry-meta {
		margin-right: auto;
	}

Changing this to margin-right: 500px made it look right at full size, but it fails when I start shrinking my screen size.

If anyone could recommend a good way to do this I’d be glad. Thanks 🙂