So I have three frames aligned vertically, and inside each there is one label, one canvas and another label aligned horizontally (all set to "-side left"). The only properties specified are "-bd 0", "-height 40", "-width 40" and "-image imagename", expand and fill are set to "1" and "both". Everything is displayed in its right position, but with a border-like grey space between the widgets. How can I get rid of that?