use QPalette Highlight color for focus highlight on all platforms

src/MainUI/PreviewWindow.cpp

@@ -552,14 +552,10 @@ bool PreviewWindow::eventFilter(QObject *object, QEvent *event)
     case QEvent::FocusIn:
       // track focus in change events of m_Preview (or one of its child focus proxies)
       if (m_use_focus_highlight) {
-          // a bit hackish as this should match what we do in main.cpp
-          // so we should probably create a sigil_constant for this value
-          // and fix both places to use it
-#ifdef Q_OS_MAC
-          m_wrapper->setStyleSheet("border: 1px solid #2B5FFE;");
-#else
-          m_wrapper->setStyleSheet("border: 1px solid red");
-#endif
+	  QString focus_qss = "border: 1px solid HIGHLIGHT_COLOR;";
+	  QString hcolor = palette().color(QPalette::Highlight).name();
+	  focus_qss.replace("HIGHLIGHT_COLOR", hcolor);
+	  m_wrapper->setStyleSheet(focus_qss);
       }
       DBG qDebug() << "focus in event: " << object;
       break;

src/main.cpp

@@ -683,16 +683,11 @@ int main(int argc, char *argv[])
         app.setStyleSheet(app.styleSheet().append(MAC_DOCK_TITLEBAR_FIX));
 #endif
 
-        // allow user to highlight focus widget
+        // allow user to highlight the focus widget
         if (settings.uiHighlightFocusWidgetEnabled()) {
             QString focus_qss = FOCUS_HIGHLIGHT_QSS;
-            // See PreviewWindow.cpp in the eventFilter routine in FocusIn
-            // where the same platform constant is used - keep in sync
-#ifdef Q_OS_MAC
-            focus_qss.replace("HIGHLIGHT_COLOR", "#2B5FFE");
-#else //Linux and Windows
-            focus_qss.replace("HIGHLIGHT_COLOR", "red");
-#endif
+	    QString hcolor = app.palette().color(QPalette::Highlight).name();
+            focus_qss.replace("HIGHLIGHT_COLOR", hcolor);
             app.setStyleSheet(app.styleSheet().append(focus_qss));
         }