Bug 1471162 - Stop using fake floating scrollbar in OSX dark theme;r=pbro

MozReview-Commit-ID: 8nFpHCWojYC

--HG--
extra : rebase_source : af1196714bdda62acf289d624de6b4c84053d016

devtools/client/shared/theme-switching.js

@@ -89,8 +89,8 @@
       loadEvents.push(loadPromise);
     }
 
-    if (os !== "win") {
-      // Windows always uses native scrollbars, other platforms still use custom floating
+    if (os !== "win" && os !== "mac") {
+      // Windows & Mac always use native scrollbars, Linux still uses custom floating
       // scrollbar implementation.
       try {
         const StylesheetUtils = require("devtools/shared/layout/utils");

devtools/client/themes/dark-theme.css

@@ -27,7 +27,8 @@ body {
   color: var(--theme-selection-color);
 }
 
-:root[platform="win"] {
+:root[platform="win"],
+:root[platform="mac"] {
   /* Set colors for native scrollbars on Windows dark theme */
   /* Other platforms support for scrollbar theming is Bug 1460109 */
   scrollbar-face-color: var(--theme-body-color-inactive);