Set margins for the front cover page
Specify the top, bottom, inside, and outside margins for the front cover page.
By default, the margins for the front cover page are the same as for the body pages—in this case 1in inside and .75in outside—because odd/right frontmatter pages use the region-body__frontmatter.odd attribute set, which in turn uses the region-body.odd attribute set. Even/left frontmatter pages use the region-body__frontmatter.even attribute set, which in turn calls the region-body.even attribute set. Both region-body.odd and region-body.even use the page-margin-inside and page-margin-outside variables, which have the values "1in" and ".75in", respectively (if you made the changes in Set page margins).
But, you want the ...