Created attachment 4938 
Screenshot edge padding

When setting the border-radius to 0, the padding between the edge of the notification and the text is quite small and this looks a little ugly to me.

See attached screenshot (top part).

The problem is, that the padding is calculated based on the border-radius option and adding 4 pixels.

Attached you will also find a patch against "master" that remedies this problem by introducing another option named "padding" which can be set in the gtkrc file like so:

style "notify-window"
{
    XfceNotifyWindow::border-color = "#ffffff"
    XfceNotifyWindow::border-radius = 0.0
    XfceNotifyWindow::border-width = 2.0
    XfceNotifyWindow::padding = 10.0   // THIS IS THE NEW OPTION
    bg[NORMAL] = "#242424"
}

See attached screenshot (bottom part).

I was trying to use GTK's built-in functionality to get the same look (using style properties), but failed. I don't know if its just me or if its not possible to do ...

The themes in this repository should not be affected by this patch as they are using the default border-radius 10. I've set the default value for the padding to be 14 (10 + 4) if not explicietely set.

Btw: I just found out, that my last patch (#9475) also introduced a local variable named "padding". I hope this is not too confusing ;-).