diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index 5a4ec02..914b830 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -12,6 +12,7 @@
         "@codemirror/commands": "^6.6.2",
         "@codemirror/lang-markdown": "^6.2.5",
         "@codemirror/state": "^6.4.1",
+        "@codemirror/theme-one-dark": "^6.1.2",
         "@codemirror/view": "^6.34.0",
         "@geist-ui/core": "^2.3.8",
         "@geist-ui/icons": "^1.0.2",
@@ -2096,6 +2097,18 @@
       "integrity": "sha512-QkEyUiLhsJoZkbumGZlswmAhA7CBU02Wrz7zvH4SrcifbsqwlXShVXg65f3v/ts57W3dqyamEriMhij1Z3Zz4A==",
       "license": "MIT"
     },
+    "node_modules/@codemirror/theme-one-dark": {
+      "version": "6.1.2",
+      "resolved": "https://registry.npmjs.org/@codemirror/theme-one-dark/-/theme-one-dark-6.1.2.tgz",
+      "integrity": "sha512-F+sH0X16j/qFLMAfbciKTxVOwkdAS336b7AXTKOZhy8BR3eH/RelsnLgLFINrpST63mmN2OuwUt0W2ndUgYwUA==",
+      "license": "MIT",
+      "dependencies": {
+        "@codemirror/language": "^6.0.0",
+        "@codemirror/state": "^6.0.0",
+        "@codemirror/view": "^6.0.0",
+        "@lezer/highlight": "^1.0.0"
+      }
+    },
     "node_modules/@codemirror/view": {
       "version": "6.34.0",
       "resolved": "https://registry.npmjs.org/@codemirror/view/-/view-6.34.0.tgz",
diff --git a/frontend/package.json b/frontend/package.json
index ec77c86..cc8e08f 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -26,6 +26,7 @@
     "@codemirror/commands": "^6.6.2",
     "@codemirror/lang-markdown": "^6.2.5",
     "@codemirror/state": "^6.4.1",
+    "@codemirror/theme-one-dark": "^6.1.2",
     "@codemirror/view": "^6.34.0",
     "@geist-ui/core": "^2.3.8",
     "@geist-ui/icons": "^1.0.2",
diff --git a/frontend/src/App.js b/frontend/src/App.js
index e2b5f85..4b1f1c2 100644
--- a/frontend/src/App.js
+++ b/frontend/src/App.js
@@ -1,4 +1,4 @@
-import React from 'react';
+import React, { useState } from 'react';
 import { GeistProvider, CssBaseline, Page } from '@geist-ui/core';
 import Header from './components/Header';
 import MainContent from './components/MainContent';
@@ -6,6 +6,7 @@ import useFileManagement from './hooks/useFileManagement';
 import './App.scss';
 
 function App() {
+  const [themeType, setThemeType] = useState('light');
   const {
     content,
     files,
@@ -18,11 +19,15 @@ function App() {
     handleSave,
   } = useFileManagement();
 
+  const toggleTheme = () => {
+    setThemeType(prevTheme => prevTheme === 'light' ? 'dark' : 'light');
+  };
+
   return (
-    <GeistProvider>
+    <GeistProvider themeType={themeType}>
       <CssBaseline />
       <Page>
-        <Header />
+        <Header currentTheme={themeType} onThemeChange={toggleTheme} />
         <Page.Content>
           <MainContent
             content={content}
diff --git a/frontend/src/components/Editor.js b/frontend/src/components/Editor.js
index ceb02bf..d6f4237 100644
--- a/frontend/src/components/Editor.js
+++ b/frontend/src/components/Editor.js
@@ -4,8 +4,9 @@ import { EditorState } from "@codemirror/state";
 import { EditorView, keymap } from "@codemirror/view";
 import { markdown } from "@codemirror/lang-markdown";
 import { defaultKeymap } from "@codemirror/commands";
+import { oneDark } from "@codemirror/theme-one-dark";
 
-const Editor = ({ content, onChange, onSave, filePath }) => {
+const Editor = ({ content, onChange, onSave, filePath, themeType }) => {
   const editorRef = useRef();
   const viewRef = useRef();
 
@@ -15,6 +16,24 @@ const Editor = ({ content, onChange, onSave, filePath }) => {
       return true;
     };
 
+    const theme = EditorView.theme({
+      "&": {
+        height: "100%",
+        fontSize: "14px",
+      },
+      ".cm-scroller": {
+        overflow: "auto",
+      },
+      ".cm-gutters": {
+        backgroundColor: themeType === "dark" ? "#1e1e1e" : "#f5f5f5",
+        color: themeType === "dark" ? "#858585" : "#999",
+        border: "none",
+      },
+      ".cm-activeLineGutter": {
+        backgroundColor: themeType === "dark" ? "#2c313a" : "#e8e8e8",
+      },
+    });
+
     const state = EditorState.create({
       doc: content,
       extensions: [
@@ -32,6 +51,8 @@ const Editor = ({ content, onChange, onSave, filePath }) => {
             onChange(update.state.doc.toString());
           }
         }),
+        theme,
+        themeType === "dark" ? oneDark : [],
       ],
     });
 
@@ -45,7 +66,7 @@ const Editor = ({ content, onChange, onSave, filePath }) => {
     return () => {
       view.destroy();
     };
-  }, [filePath]);
+  }, [filePath, themeType]);
 
   useEffect(() => {
     if (viewRef.current && content !== viewRef.current.state.doc.toString()) {
diff --git a/frontend/src/components/Header.js b/frontend/src/components/Header.js
index 6fa632c..585d188 100644
--- a/frontend/src/components/Header.js
+++ b/frontend/src/components/Header.js
@@ -3,7 +3,7 @@ import { Page, Text, User, Button, Spacer } from '@geist-ui/core';
 import { Settings as SettingsIcon } from '@geist-ui/icons';
 import Settings from './Settings';
 
-const Header = () => {
+const Header = ({ currentTheme, onThemeChange }) => {
   const [settingsVisible, setSettingsVisible] = useState(false);
 
   const openSettings = () => setSettingsVisible(true);
@@ -16,7 +16,12 @@ const Header = () => {
       <User src="https://via.placeholder.com/40" name="User" />
       <Spacer w={0.5} />
       <Button auto icon={<SettingsIcon />} onClick={openSettings} />
-      <Settings visible={settingsVisible} onClose={closeSettings} />
+      <Settings 
+        visible={settingsVisible} 
+        onClose={closeSettings} 
+        currentTheme={currentTheme}
+        onThemeChange={onThemeChange}
+      />
     </Page.Header>
   );
 };
diff --git a/frontend/src/components/MainContent.js b/frontend/src/components/MainContent.js
index 836c4ec..fcdb1e5 100644
--- a/frontend/src/components/MainContent.js
+++ b/frontend/src/components/MainContent.js
@@ -1,5 +1,5 @@
 import React, { useState } from 'react';
-import { Grid, Breadcrumbs, Tabs, Dot } from '@geist-ui/core';
+import { Grid, Breadcrumbs, Tabs, Dot, useTheme } from '@geist-ui/core';
 import { Code, Eye } from '@geist-ui/icons';
 import Editor from './Editor';
 import FileTree from './FileTree';
@@ -16,6 +16,7 @@ const MainContent = ({
   onSave,
 }) => {
   const [activeTab, setActiveTab] = useState('source');
+  const { type: themeType } = useTheme();
 
   const renderBreadcrumbs = () => {
     if (!selectedFile) return null;
@@ -60,6 +61,7 @@ const MainContent = ({
               onChange={onContentChange} 
               onSave={onSave}
               filePath={selectedFile}
+              themeType={themeType}
             />
           ) : (
             <MarkdownPreview content={content} />
diff --git a/frontend/src/components/Settings.js b/frontend/src/components/Settings.js
index 0d3da66..153a338 100644
--- a/frontend/src/components/Settings.js
+++ b/frontend/src/components/Settings.js
@@ -1,14 +1,12 @@
 import React, { useState } from 'react';
-import { Modal, Input, Toggle, Select, Spacer, Button } from '@geist-ui/core';
+import { Modal, Input, Toggle, Spacer, Button, Text } from '@geist-ui/core';
 
-const Settings = ({ visible, onClose }) => {
-  const [theme, setTheme] = useState('light');
+const Settings = ({ visible, onClose, currentTheme, onThemeChange }) => {
   const [fontSize, setFontSize] = useState('14');
   const [autoSave, setAutoSave] = useState(false);
 
   const handleSubmit = () => {
     const settings = {
-      theme,
       fontSize,
       autoSave,
     };
@@ -21,14 +19,13 @@ const Settings = ({ visible, onClose }) => {
     <Modal visible={visible} onClose={onClose}>
       <Modal.Title>Settings</Modal.Title>
       <Modal.Content>
-        <Select 
-          label="Theme" 
-          value={theme} 
-          onChange={(val) => setTheme(val)}
+        <Text>Theme</Text>
+        <Toggle 
+          checked={currentTheme === 'dark'}
+          onChange={() => onThemeChange()}
         >
-          <Select.Option value="light">Light</Select.Option>
-          <Select.Option value="dark">Dark</Select.Option>
-        </Select>
+          Dark Mode
+        </Toggle>
         <Spacer h={0.5} />
         <Input 
           label="Font Size" 
diff --git a/frontend/src/customTheme.js b/frontend/src/customTheme.js
new file mode 100644
index 0000000..8adb184
--- /dev/null
+++ b/frontend/src/customTheme.js
@@ -0,0 +1,27 @@
+import { Themes } from '@geist-ui/core'
+
+const customDarkTheme = Themes.createFromLight({
+  type: 'custom-dark',
+  palette: {
+    background: '#1e1e1e',
+    foreground: '#d4d4d4',
+    selection: '#2c313a',
+    secondary: '#858585',
+    code: '#d4d4d4',
+    border: '#333333',
+    success: '#4EC9B0',
+    warning: '#9CDCFE',
+    error: '#F44747',
+  },
+  expressiveness: {
+    dropdownBoxShadow: '0 0 0 1px #333333',
+    shadowSmall: '0 0 0 1px #333333',
+    shadowMedium: '0 0 0 1px #333333',
+    shadowLarge: '0 0 0 1px #333333',
+  },
+})
+
+export const customTheme = {
+  light: Themes.light,
+  dark: customDarkTheme,
+}
\ No newline at end of file