gui2: cleanup of the text box widget design

This reduces border size as well as removes a hack related to transparent
backgrounds and text rendering. I can't observe any issue with text AA
using semi-transparent backgrounds anymore.

data/gui/default/widget/text_box_default.cfg

@@ -15,19 +15,12 @@
 	[/rectangle]
 #enddef
 
-#
-# Text antialiasing doesn't work as expected when rendering over a rectangle
-# filled with an alpha < 255 color, so instead of using
-# GUI__BACKGROUND_COLOR_ENABLED and GUI__BACKGROUND_COLOR_DISABLED for the
-# textbox background, use fully opaque colors that correspond to the averages
-# one would get with those two macros.
-#
 #define _GUI_TEXTBOX_BACKGROUND_ENABLED
-	{_GUI_DRAW_BACKGROUND ("10, 13, 22, 255")}
+	{_GUI_DRAW_BACKGROUND ({GUI__BACKGROUND_COLOR_ENABLED})}
 #enddef
 
 #define _GUI_TEXTBOX_BACKGROUND_DISABLED
-	{_GUI_DRAW_BACKGROUND ("28, 31, 41, 255")}
+	{_GUI_DRAW_BACKGROUND ({GUI__BACKGROUND_COLOR_DISABLED})}
 #enddef
 
 #define _GUI_DRAW_BORDER COLOR
@@ -37,35 +30,13 @@
 		w = "(width)"
 		h = "(height)"
 
-		border_thickness = 3
-		border_color = "55, 55, 55, 192"
-
-	[/rectangle]
-
-	[rectangle]
-		x = 1
-		y = 1
-		w = "(if(width < 2, 0, width - 2))"
-		h = "(if(height < 2, 0, height - 2))"
-
 		border_thickness = 1
 		border_color = {COLOR}
 
 	[/rectangle]
 #enddef
 
 #define _GUI_DRAW_TEXT SIZE COLOR
-	[rectangle]
-		x = "(text_x_offset + selection_offset)"
-		y = "(text_y_offset)"
-		w = "(selection_width)"
-		h = "(text_font_height)"
-
-		border_thickness = 0
-		fill_color = "21, 53, 80, 255"
-
-	[/rectangle]
-
 	[text]
 		x = "(text_x_offset)"
 		y = "(text_y_offset)"