Configure canvas for a new selection.

def _show_selection(self, text, bbox):
        """Configure canvas for a new selection."""
        x, y, width, height = bbox

        textw = self._font.measure(text)

        canvas = self._canvas
        canvas.configure(width=width, height=height)
        canvas.coords(canvas.text, width - textw, height / 2 - 1)
        canvas.itemconfigure(canvas.text, text=text)
        canvas.place(in_=self._calendar, x=x, y=y)