If you see your background image and your banner overlapped in your browser, masking the visibility of the rest of your campaign content,this FAQ shoulh help you to solve the problem.
It is often a simple zoom/unzoom in your browser which causes a display bug of the banner and the background image. You can easily reset the zoom of your default browser by clicking:
Mac: (cmd) + (+) = zoom et (cmd) + (-) = unzoom
PC: Ctrl + 0
You will find here below more information on the browser zoom:
Mozilla Firefox: https://support.mozilla.org/fr/kb/taille-police-zoom-augmenter-taille-pages
Google Chrome: https://support.google.com/chrome/answer/96810?hl=fr
Internet Explorer: https://support.microsoft.com/fr-be/help/17456/windows-internet-explorer-ease-of-access-options