Missing space when I change cell background color in SlickGrid?

I tried to change the background color of the cell using custom formatting, for example:

var myCellFormatter = function(row, cell, value, columnDef, dataContext) {
    if ((row + cell) % 5 == 1) {
        return "<div style='background-color:green'>" + value + "</div>";
    } else {
        return value;
    }
};

but it does not color the whole cell. There is some space between the cell divand divthe formatting.

How can I color the whole cell?