HI Mark,
The correct approach for this is to have the widest content size that you need in the Theme Options.
Then please go to each page and use the Cornerstone settings button to make the page full width. Click the settings button at the left bottom of the screen while you are on the page using the Cornerstone:
A pop up will appear. Click the Page Settings tab and select the Blank - No Container, Header, Footer option:
Then add a section. In the section click the Row settings so that you can access the settings of the row:
Then click the Customize tab and click the Element CSS option and add teh code below:
$el {
max-width: 500px !important;
}
Change 500px to whatever maximum width you like.
This way, you can control each row maximum width. For more information about the Element CSS feature please click here.
I know this is not an ideal way to have control over the maximum width for specific pages, but at the moment you have that only choice. Our development team is in the process of releasing teh layout builder which will ring the CSS Flex and Grid to the builder. Then you will have better control over such cases.
Click here for more information about the release roadmap of the X theme.
Thank you.