Thank you for that answer Marius ! Unfortunately it didn't work out well (despite trying other values as you said) :
Attached you will see that menus overlap the title (image 1) or when you narrow the window, they overlap more and one menu can't fit in the length (image2).
Best would be to two fixed menus fixed from the right of the title, and the two others fixed from its left. Whenever you spread the window, the menu keeps a pair of menus as "wings"
Thanks for your help.
I chose to use an horizontal top frame menu. with 4 elements.
How can I precisely space these 4 around the website title (jpg) so that they're all centered on one line and the menus don't cross the title, please ? Title in the middle, two menus on each side.