LibGUI: Use different color for GlyphMapWidget background

This patch makes background a bit darkened so that it is possible to
distinguish out of range area from glyphs that are just not drawn.

The default background color is also changed to Window so that it looks
good in more themes.

Userland/Libraries/LibGUI/GlyphMapWidget.cpp

@@ -104,7 +104,7 @@ void GlyphMapWidget::paint_event(PaintEvent& event)
     painter.add_clip_rect(event.rect());
 
     painter.set_font(font());
-    painter.fill_rect(widget_inner_rect(), palette().inactive_window_title());
+    painter.fill_rect(widget_inner_rect(), palette().window().darkened(0.8f));
 
     int scroll_steps = vertical_scrollbar().value() / vertical_scrollbar().step();
     int first_visible_glyph = scroll_steps * columns();
@@ -130,7 +130,8 @@ void GlyphMapWidget::paint_event(PaintEvent& event)
         } else if (auto* emoji = Gfx::Emoji::emoji_for_code_point(glyph)) {
             painter.fill_rect(outer_rect, Gfx::Color { 255, 150, 150 });
             painter.draw_emoji(inner_rect.location(), *emoji, font());
-        }
+        } else
+            painter.fill_rect(outer_rect, palette().window());
     }
     painter.draw_focus_rect(get_outer_rect(m_active_glyph), Gfx::Color::Black);
 }