Use always system appearance in editor view (close #947)

CHANGELOG.md

@@ -13,6 +13,7 @@ Change Log
 ### Improvements
 
 - Apply the change of “show other invisible characters” option immediately to the editors.
+- Use the system appearance in the input candidate window even when the theme has a dark background color.
 - Give feedback about the search result in VoiceOver.
 - Improve the behavior of Opt+Arrow shortcut series to stop the by punctuation marks, such as `.` and  `:`.
 - Optimize the performance of finding the matching brace to highlight.

CotEditor/Sources/EditorTextView.swift

@@ -1306,11 +1306,7 @@ final class EditorTextView: NSTextView, Themable, CurrentLineHighlighting, Multi
         }
         
         // set scroller color considering background color
-        if #available(macOS 10.14, *) {
-            self.enclosingScrollView?.appearance = NSAppearance(named: theme.isDarkTheme ? .darkAqua : .aqua)
-        } else {
-            self.enclosingScrollView?.scrollerKnobStyle = theme.isDarkTheme ? .light : .default
-        }
+        self.enclosingScrollView?.scrollerKnobStyle = theme.isDarkTheme ? .light : .default
         
         self.setNeedsDisplay(self.visibleRect, avoidAdditionalLayout: true)
     }