selectively set content width

Leo, I am so grateful for the help you have offered!
I wish there was a way to export the inspector.
This is a lame substitute but at least illustrates the order and interplay of elements involved:

https://www.dropbox.com/s/cpurdvof360fkld/GP-inspector.png?dl=1

Steve

What if you apply the custom width to all grid-container classes on the page?

body .grid-container {
    max-width: 2000px;
}

I think I got it.

.entry-content {
    max-width: 1200px !important;
}

I hadn't resorted to the heavy handed !important before.
I appreciate that this was frustrating for you since you weren't able to interact with it live online. Thanks for your patience. Once this goes live I may be back, but hopefully not. I have more than one site I'm hoping to use this layout pattern for, so the effort was worth it for me.
Gratefully,
Steve

You're welcome :)

Definitely don't want to use too much !important.

Let us know if you want us to take a look at it once it's live.