Hi, Thanks for your help. Your solution works but I need more "fine tuning" on this background.
If you want the background on chapter pages etc. it makes sense to integrate the background in a slightly different way but more details about the layout needed for this to find the best solution. So, I'll explain in more details the structure of my layout.
The idea is that the pages are presented side-by-side. Visually we have 4 columns. - The last one (right, on the right page) is the main text. - The third column (left, on the right page) is used for the figures (images, graphs, diagrams, etc.) - The second column (right, on the left page) is used to discuss some points of the main text. Like advanced stuff, debate, historical notes, etc) - The first one (left, on the left page) have some light gray background and is an area for FAQ about the topic. The title of each double page is on the right page, aligned with the left column of the right page. The second column (right, on the left page) may have a title defining the topic of this column. Regards, Antoine