How can I add my own code to dhtmlxgrid.css which comes as part of the package? When I go to source I cannot edit anything over there. Please reply as soon as possible.
You can add the custom css file, in which you can redefine the same rules but with necessary values ( if it will be included in page after default css file )
In such case you will be able to use your custom styles, and will not have problem when ( if ) updating to new build of grid.