Bug 1471162 - Style codemirror scrollbar corners correctly in dark-theme;r=gl

MozReview-Commit-ID: 875fTgrmpJO

--HG--
extra : rebase_source : 6291c64f72fc33a4ecb99130085410b1d09628cf

devtools/client/debugger/new/dist/debugger.css

@@ -247,10 +247,6 @@ body {
   border-radius: 8px;
   background: rgba(113, 113, 113, 0.5);
 }
-
-:root.theme-dark .CodeMirror-scrollbar-filler {
-  background: transparent;
-}
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */

devtools/client/sourceeditor/codemirror/mozilla.css

@@ -291,3 +291,8 @@ selector in floating-scrollbar-light.css across all platforms. */
 .CodeMirror-Tern-fhint-guess {
   opacity: .7;
 }
+
+/* Override the background-color: white applied to filler elements in codemirror.css */
+.CodeMirror-scrollbar-filler, .CodeMirror-gutter-filler {
+  -moz-appearance: scrollcorner;
+}