How to fix both first row and first column ?

realtebo

I've a large table. (>50 cols, >100 rows).

i'm using fixed header to keep first row fixed ad top. But i'm not able to enable the first COLUMN to stay fixed when user scroll horizontally.

This is my initialization code:

$('#order_proposal_table').DataTable({
        'pageLength'    : 500,
        'fixedHeader'    : true,
        'fixedColumns':   {
            leftColumns: 1,
        },
        'sDom'          : 'lprtip ', // default was lfrtip, i repeat pagination both on top and on bottom
        'lengthMenu'    : [[10,25,50,100,250,500,-1], [10,25,50,100,250,500,'Tutte']],
        'language'      : {
            'url': '//cdn.datatables.net/plug-ins/1.10.10/i18n/Italian.json',
        }
    }); 

Do I need some CSS tricks to enable horizontal scrolling with fixed column?