First, awesome work on this builder, works very well !
Now I would like my individual page to have a header that contain both the page Title (H1) + a full width background image (background: cover). How can I do that ? See this printscreen :
You should be able to add a full-width row even with the sidebar by using the sidebar module. You can add it under Add Content > Advance Modules > Sidebar on a row and then add the full-width header on top of it.