A few misc fixes after the grand button/color refactor:

- Always draw traffic signal stage numbers as white, even in day mode
- Always draw loading screen text as white, in any theme
- Double the scrollbar thickness from 4px to 8px (still way thinner than
  the original design)

[rebuild] [release]

map_gui/src/render/traffic_signal.rs

@@ -208,7 +208,7 @@ pub fn draw_stage_number(
         Circle::new(center, radius).to_polygon(),
     );
     batch.append(
-        Text::from(Line(format!("{}", idx + 1)))
+        Text::from(Line(format!("{}", idx + 1)).fg(Color::WHITE))
             .render_autocropped(prerender)
             .scale(0.075)
             .centered_on(center),

widgetry/src/event_ctx.rs

@@ -186,7 +186,8 @@ impl<'a> EventCtx<'a> {
             .centered_vert(),
             Widget::draw_batch(
                 self,
-                txt.inner_render(&self.prerender.assets, svg::LOW_QUALITY),
+                txt.change_fg(Color::WHITE)
+                    .inner_render(&self.prerender.assets, svg::LOW_QUALITY),
             )
             .container()
             .fill_width()

widgetry/src/widgets/slider.rs

@@ -24,7 +24,7 @@ enum Style {
     Area { width: f64 },
 }
 
-pub const SCROLLBAR_BG_WIDTH: f64 = 4.0;
+pub const SCROLLBAR_BG_WIDTH: f64 = 8.0;
 pub const AREA_SLIDER_BG_WIDTH: f64 = 10.0;
 
 impl Style {