Margin error with Portfolio post type and no widgets

[davidakennedy]

Creating ticket from 39573 from WordPress.org user ashercantrell:

Using Portfolio projects in Twenty Sixteen on a site with no widgets in the sidebar leads to some strange margin issues. There's a lot of white space to the side of the content, making the text start nearly in the center, like this:

[[Image(https://cldup.com/_TStsYRC4r.png)]]

If you inspect the area, you can see some very odd margins in the CSS:

[[Image(https://cldup.com/lzji2hWK-A.png)]]

If that's difficult to read, it says there's a 389.141 left margin and a -1111.840 right margin, which is causing the unusual white space.

I did find a workaround: Adding any sidebar widgets, including a blank text widget, will correct the margin issue:

See: https://cldup.com/1KIYImUndw.png

The margins with the widget(s) in place look like this:

See: https://cldup.com/lzji2hWK-A.png