I changed an Edit Form in Sharepoint (included a script editor web part) to enlarge multi value fields list boxes (they were to small in width) and it worked (inserted code snippet).
However, if i create a new edit form using sharepoint designer (to set control mode to "Display" in some columns) these multi-value fields are back to small and not enlarged (width) and i don“t know how to do it... sorry not a guru in javascript/html/sharepoint...
Alternate approach to be considered : set control mode to "Display" directly in sharepoint without using designer.
thanks a lot for your help Nuno