Container Width: 811px

You can add your own custom CSS.

body .grid-container {
      max-width: 811px;
}

Yeah, but the options will generate an inline style, right?

So those “win” or I’m I wrong?

Nope, the styles aren't inline :)

If you add the CSS to your child theme or using the plugin in my signature, it will "win" over the other ones.

oops, I was in the wrong child theme...

Got it all working? :)

Yes it's all working fine.
I'm just curious and don't quiet understand.

You know, if I'm customizing "Element Spacing" for example, it will change the inline style. Also the "Container Width" does in fact create an inline style but it's overwritten by the stylesheet as I interpret it from the "Inspect Element" view in Firefox.

I'm just trying out how to customize the best way. About half a year ago I added background image support for header for the theme customizer. I didn't realize this is already available via Plugin (or maybe it even wasn't then). Well, I learned something even if I forgot most of it already.

Can you confirm that I understand it right:
Theme Options via customizer get saved in the wp_options table.
If I change theme and/or delete the GP Premium plugin the customizing values stay in the table but can't be edited anymore. Changing back will use the "old" customizations.
Correct?

That's correct. The options save to wp_options, and will stay there unless you delete them.

When you use a different theme, they will stay there in case you return to GP, but won't be used anymore.