Bug 1941755 - Tweak checked radio rendering as per UX feedback. r=mstange

Differential Revision: https://phabricator.services.mozilla.com/D234341

widget/Theme.cpp

@@ -652,14 +652,13 @@ void Theme::PaintRadioControl(PaintBackendData& aPaintData,
   }
 
   if (aState.HasState(ElementState::CHECKED)) {
-    const CSSCoord kInnerBorderWidth = 2.0f;
     LayoutDeviceRect rect(aRect);
-    auto width = LayoutDeviceCoord(
-        ThemeDrawing::SnapBorderWidth(kInnerBorderWidth, aDpiRatio));
-    rect.Deflate(width);
-
-    PaintStrokedCircle(aPaintData, rect, backgroundColor, checkColor,
-                       kInnerBorderWidth, aDpiRatio);
+    // Make the inner white dot take ~half of the checkbox (snapped to device
+    // pixels).
+    rect.Deflate(std::max(LayoutDeviceIntCoord(1),
+                          (LayoutDeviceCoord(rect.width) * 0.25f).Truncated()));
+    PaintStrokedCircle(aPaintData, rect, checkColor, sTransparent, 0,
+                       aDpiRatio);
   }
 
   if (aState.HasState(ElementState::FOCUSRING)) {