Describe the bug
With the 0.18 design, a process banner seems to be automatically compressed to 1000 px width while the section might be wider on laptop/desktop screens. Banners appear in low definition on good quality/retina screens. We used to have better definition in 0.12 I think. Can we improve this?

To Reproduce
Steps to reproduce the behavior:

1. Go to a process page (for example https://participer.valdemarne.fr/processes/budgetcitoyen)
2. Inspect sizes with your browser.