Middle Column: Make empty background draggable in Electron (#3751)

src/components/middle/MiddleColumn.module.scss

@@ -41,6 +41,10 @@
     }
   }
 
+  &.draggable {
+    -webkit-app-region: drag;
+  }
+
   &.customBgImage.blurred::before {
     filter: blur(12px);
   }

src/components/middle/MiddleColumn.tsx

@@ -23,6 +23,7 @@ import {
   MAX_SCREEN_WIDTH_FOR_EXPAND_PINNED_MESSAGES,
   EDITABLE_INPUT_ID,
   EDITABLE_INPUT_CSS_SELECTOR,
+  IS_ELECTRON,
 } from '../../config';
 import {
   IS_ANDROID, IS_IOS, IS_TRANSLATION_SUPPORTED, MASK_IMAGE_DISABLED,
@@ -413,6 +414,7 @@ function MiddleColumn({
     backgroundColor && styles.customBgColor,
     customBackground && isBackgroundBlurred && styles.blurred,
     isRightColumnShown && styles.withRightColumn,
+    IS_ELECTRON && !(renderingChatId && renderingThreadId) && styles.draggable,
   );
 
   const messagingDisabledClassName = buildClassName(