Hi Prisca…first, if this is related to a specific theme, please post it in the appropriate forum category; so with that in mind, what theme is this for?
Now the bad news is that your questions relate to performing “customization” which support does not cover, but what I would suggest is setup a development site with the theme, and start modifying the code to achieve the results you want. I can tell you that moving a menu container to be below a logo will require you to have coding skills because you will need to move html, php code, and also modify css. Changing and or adding styling to images will also require you to have some html and css basics of understanding as well. Your other option would be to find someone who might be able to make these kind of changes.
No worries… I really and truly wish I can help everyone who wants to do custom changes with themes, but anything “custom” someone wants to do falls out of support. The closest I could do is point out where code is located in files or what files to look into and then let the person have fun with code.
Regarding adding a background to menu links, what I can do is provide you with the container you can do that to if it’s the full container that you want to add it to.
That would be great if you could tell me which classes or ID I have to go to edit the menu to put a bg on links (top menu to li – not the dropdown) and mainly – which class I should find to add a border to ALL images but the logo and icons. That’s important for me. I like borders around images. I added a border to the gallery class and it put a border around the div – not around the image itself.
So if you could just give me the exact class or id where I should add the border that would be great.
Sorry..forgot the images. This will depend on where and what as images in the theme will depend on how they are being added. But to give you a direction, in the style.css is this batch of empty classes, ready for styling around line 1424: