Add file area (drop main file into main container)

The area to drop main file is only a rectangle at the top, when it should be the the almost entire area of the main container - to avoid the user to drop on the white space and leave page, without wanting.
Note that on Firefox there is no empty space between the drop area and the other boxes below (see attached screenshot).

• Distribution: nuxeo-server-9.3-I20171115_2314-tomcat
• Browser: Safari, Chrome.