diff --git a/main.py b/main.py
index aa6123b..9e6d119 100644
--- a/main.py
+++ b/main.py
@@ -317,7 +317,12 @@ class MarkdownEditor(QMainWindow):
         view_menu = menu_bar.addMenu("&View")
         self.add_actions_to_menu(view_menu, [
             ("Toggle Split View Mode", self.toggle_split_view),
-            ("Toggle Toolbar", self.toggle_toolbar)
+            ("Toggle Toolbar", self.toggle_toolbar),
+            ("Theme", [
+                ("Dark", lambda: self.change_theme("dark")),
+                ("Light", lambda: self.change_theme("light")),
+                ("System", lambda: self.change_theme("system"))
+            ])
         ])
 
         window_menu = menu_bar.addMenu("&Window")
@@ -335,17 +340,17 @@ class MarkdownEditor(QMainWindow):
         ])
 
     def add_actions_to_menu(self, menu, actions):
-        """
-        Add actions to a given menu.
-
-        Args:
-            menu (QMenu): The menu to which actions will be added.
-            actions (list of tuples): Each tuple contains the text for the menu item and the handler function.
-        """
-        for action_text, action_handler in actions:
-            action = QAction(action_text, self)
-            action.triggered.connect(action_handler)
-            menu.addAction(action)
+        for action_text, action_func in actions:
+            if isinstance(action_func, list):  # Submenu
+                submenu = menu.addMenu(action_text)
+                for sub_action_text, sub_action_func in action_func:
+                    sub_action = QAction(sub_action_text, self)
+                    sub_action.triggered.connect(sub_action_func)
+                    submenu.addAction(sub_action)
+            else:
+                action = QAction(action_text, self)
+                action.triggered.connect(action_func)
+                menu.addAction(action)
 
     def create_tool_bar(self):
         """
@@ -666,8 +671,64 @@ class MarkdownEditor(QMainWindow):
             else:
                 QMessageBox.critical(self, "Directory Selection Error", "Invalid directory path")
 
-    def change_theme(self):
-        pass
+    def change_theme(self, theme):
+        if theme == "dark":
+            self.apply_dark_theme()
+        elif theme == "light":
+            self.apply_light_theme()
+        elif theme == "system":
+            self.apply_system_theme()
+
+    def apply_dark_theme(self):
+        dark_stylesheet = """
+        QMainWindow {
+            background-color: #282c34; /* Dark gray background */
+            color: #abb2bf; /* Light gray text */
+        }
+        QMenuBar {
+            background-color: #21252b; /* Slightly darker gray for menu bar */
+            color: #abb2bf;
+        }
+        QMenuBar::item {
+            background-color: #21252b;
+            color: #abb2bf;
+        }
+        QMenuBar::item:selected { /* when selected using mouse or keyboard */
+            background-color: #282c34;
+        }
+        QTextEdit, QTreeView {
+            background-color: #282c34;
+            color: #abb2bf;
+        }
+        """
+        self.setStyleSheet(dark_stylesheet)
+
+    def apply_light_theme(self):
+        light_stylesheet = """
+        QMainWindow {
+            background-color: #fafafa; /* Very light gray, almost white */
+            color: #383a42; /* Dark gray text */
+        }
+        QMenuBar {
+            background-color: #f0f0f0; /* Light gray for menu bar */
+            color: #383a42;
+        }
+        QMenuBar::item {
+            background-color: #f0f0f0;
+            color: #383a42;
+        }
+        QMenuBar::item:selected {
+            background-color: #fafafa;
+        }
+        QTextEdit, QTreeView {
+            background-color: #fafafa;
+            color: #383a42;
+        }
+        """
+        self.setStyleSheet(light_stylesheet)
+
+    def apply_system_theme(self):
+        self.setStyleSheet("")
 
     def open_settings(self):
         pass