Bug 1742796 - Use a more transparent color for dark mode / Android selection. r=geckoview-reviewers,owlish

This prevents contrast issues with colors that are very similar to the
selection background.

See before / after screenshots. Selection on higher-contrasting
foregrounds still looks good.

This is the alpha channel that e.g., Bugzilla uses on dark mode
(so I didn't just mint it).

Differential Revision: https://phabricator.services.mozilla.com/D132022

widget/android/nsLookAndFeel.cpp

@@ -104,7 +104,7 @@ nsresult nsLookAndFeel::NativeGetColor(ColorID aID, ColorScheme aColorScheme,
       nscolor accent =
           Color(ColorID::MozAccentColor, aColorScheme, UseStandins::No);
       aColor =
-          NS_RGBA(NS_GET_R(accent), NS_GET_G(accent), NS_GET_B(accent), 153);
+          NS_RGBA(NS_GET_R(accent), NS_GET_G(accent), NS_GET_B(accent), 78);
       return NS_OK;
     }
     case ColorID::Highlighttext:

widget/nsXPLookAndFeel.cpp

@@ -697,7 +697,7 @@ Maybe<nscolor> nsXPLookAndFeel::GenericDarkColor(ColorID aID) {
       color = NS_RGB(91, 91, 102);
       break;
     case ColorID::Highlight:
-      color = NS_RGBA(0, 221, 255, 153);
+      color = NS_RGBA(0, 221, 255, 78);
       break;
     case ColorID::Highlighttext:
       color = NS_SAME_AS_FOREGROUND_COLOR;