opt: use const variable

flutter/lib/consts.dart

@@ -15,6 +15,11 @@ const int kMobileDefaultDisplayHeight = 1280;
 const int kDesktopDefaultDisplayWidth = 1080;
 const int kDesktopDefaultDisplayHeight = 720;
 
+/// [kDefaultScrollAmountMultiplier] indicates how many rows can be scrolled after a minimum scroll action of mouse
+const kDefaultScrollAmountMultiplier = 3.0;
+const kFullScreenEdgeSize = 1.0;
+const kWindowEdgeSize = 4.0;
+
 const kInvalidValueStr = "InvalidValueStr";
 
 /// flutter/packages/flutter/lib/src/services/keyboard_key.dart -> _keyLabels

flutter/lib/desktop/pages/desktop_tab_page.dart

@@ -60,7 +60,9 @@ class _DesktopTabPageState extends State<DesktopTabPage> {
     return Platform.isMacOS
         ? tabWidget
         : Obx(() => DragToResizeArea(
-            resizeEdgeSize: fullscreen.value ? 1.0 : 4.0, child: tabWidget));
+            resizeEdgeSize:
+                fullscreen.value ? kFullScreenEdgeSize : kWindowEdgeSize,
+            child: tabWidget));
   }
 
   void onAddSetting() {

flutter/lib/desktop/pages/file_manager_tab_page.dart

@@ -4,6 +4,7 @@ import 'dart:io';
 import 'package:desktop_multi_window/desktop_multi_window.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_hbb/common.dart';
+import 'package:flutter_hbb/consts.dart';
 import 'package:flutter_hbb/desktop/pages/file_manager_page.dart';
 import 'package:flutter_hbb/desktop/widgets/tabbar_widget.dart';
 import 'package:flutter_hbb/utils/multi_window_manager.dart';
@@ -81,7 +82,7 @@ class _FileManagerTabPageState extends State<FileManagerTabPage> {
     return Platform.isMacOS
         ? tabWidget
         : SubWindowDragToResizeArea(
-            resizeEdgeSize: 4.0,
+            resizeEdgeSize: kWindowEdgeSize,
             windowId: windowId(),
             child: tabWidget,
           );

flutter/lib/desktop/pages/port_forward_tab_page.dart

@@ -4,6 +4,7 @@ import 'dart:io';
 import 'package:desktop_multi_window/desktop_multi_window.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_hbb/common.dart';
+import 'package:flutter_hbb/consts.dart';
 import 'package:flutter_hbb/desktop/pages/port_forward_page.dart';
 import 'package:flutter_hbb/desktop/widgets/tabbar_widget.dart';
 import 'package:flutter_hbb/utils/multi_window_manager.dart';
@@ -92,7 +93,7 @@ class _PortForwardTabPageState extends State<PortForwardTabPage> {
     return Platform.isMacOS
         ? tabWidget
         : SubWindowDragToResizeArea(
-            resizeEdgeSize: 4.0,
+            resizeEdgeSize: kWindowEdgeSize,
             windowId: windowId(),
             child: tabWidget,
           );

flutter/lib/desktop/pages/remote_tab_page.dart

@@ -143,7 +143,8 @@ class _ConnectionTabPageState extends State<ConnectionTabPage> {
     return Platform.isMacOS
         ? tabWidget
         : Obx(() => SubWindowDragToResizeArea(
-            resizeEdgeSize: fullscreen.value ? 1.0 : 4.0,
+            resizeEdgeSize:
+                fullscreen.value ? kFullScreenEdgeSize : kWindowEdgeSize,
             windowId: windowId(),
             child: tabWidget));
   }

flutter/lib/desktop/widgets/scroll_wrapper.dart

 import 'package:flutter/widgets.dart';
+import 'package:flutter_hbb/consts.dart';
 import 'package:flutter_improved_scrolling/flutter_improved_scrolling.dart';
 
 class DesktopScrollWrapper extends StatelessWidget {
@@ -13,8 +14,8 @@ class DesktopScrollWrapper extends StatelessWidget {
     return ImprovedScrolling(
       scrollController: scrollController,
       enableCustomMouseWheelScrolling: false,
-      customMouseWheelScrollConfig:
-          const CustomMouseWheelScrollConfig(scrollAmountMultiplier: 3.0),
+      customMouseWheelScrollConfig: const CustomMouseWheelScrollConfig(
+          scrollAmountMultiplier: kDefaultScrollAmountMultiplier),
       child: child,
     );
   }