diff --git a/main/common.ts b/main/common.ts
index dba4e3d..fda9c4e 100644
--- a/main/common.ts
+++ b/main/common.ts
@@ -9,6 +9,7 @@ export const APP_ICON = path.join(__dirname, '..', 'resources', 'icon', 'icon.pn
 export const PRELOAD_JS = path.join(__dirname, '..', 'renderer', 'preload.js');
 export const DATA_DIR = app.getPath('userData');
 export const CONFIG_FILE = path.join(DATA_DIR, 'config.json');
+export const USER_CSS = path.join(DATA_DIR, 'user.css');
 
 export function trayIcon(color: string) {
     return path.join(__dirname, '..', 'resources', 'icon', `tray-icon-${
diff --git a/main/config.ts b/main/config.ts
index 63ae8d9..bc514c5 100644
--- a/main/config.ts
+++ b/main/config.ts
@@ -17,6 +17,7 @@ export interface Config {
     normal_window: boolean;
     zoom_factor: number;
     accounts: Account[];
+    chromium_sandbox: boolean;
     keymaps: {[key: string]: string};
 }
 
@@ -31,6 +32,7 @@ function makeDefaultConfig(): Config {
         hide_menu: false,
         normal_window: menubarBroken,
         zoom_factor: 0.9,
+        chromium_sandbox: true,
         accounts: [{
             name: '',
             host: '',
diff --git a/main/index.ts b/main/index.ts
index 787edb4..1f09183 100644
--- a/main/index.ts
+++ b/main/index.ts
@@ -17,7 +17,7 @@ process.on('unhandledRejection', (reason: string) => {
             buttons: ['OK'],
             message: msg,
         }, () => {
-            qpp.quit();
+            app.quit();
         })
     });
     log.error(msg);
diff --git a/main/window.ts b/main/window.ts
index 55dace3..433ba82 100644
--- a/main/window.ts
+++ b/main/window.ts
@@ -1,10 +1,11 @@
+import * as fs from 'fs';
 import {app, BrowserWindow, shell, dialog, Menu} from 'electron';
 import windowState = require('electron-window-state');
 import * as menubar from 'menubar';
 import {Config, Account} from './config';
 import {partitionForAccount} from './account_switcher';
 import log from './log';
-import {IS_DEBUG, IS_DARWIN, IS_WINDOWS, IS_LINUX, APP_ICON, PRELOAD_JS, trayIcon} from './common';
+import {IS_DEBUG, IS_DARWIN, IS_WINDOWS, IS_LINUX, APP_ICON, PRELOAD_JS, USER_CSS, trayIcon} from './common';
 
 const ELECTRON_ISSUE_9230 = IS_WINDOWS || IS_LINUX;
 
@@ -93,6 +94,21 @@ export default class Window {
     }
 }
 
+function applyUserCss(win: Electron.BrowserWindow, config: Config) {
+    if (config.chromium_sandbox) {
+        log.debug('User CSS is disabled because Chromium sandbox is enabled');
+        return;
+    }
+    fs.readFile(USER_CSS, 'utf8', (err, css) => {
+        if (err) {
+            log.debug('Failed to load user.css: ', err.message);
+            return;
+        }
+        win.webContents.insertCSS(css);
+        log.debug('Applied user CSS:', USER_CSS);
+    });
+}
+
 function startNormalWindow(account: Account, config: Config): Promise<Window> {
     log.debug('Setup a normal window');
     return new Promise<Window>(resolve => {
@@ -108,10 +124,10 @@ function startNormalWindow(account: Account, config: Config): Promise<Window> {
             icon: APP_ICON,
             show: false,
             useContentSize: true,
-            autoHideMenuBar: config.hide_menu,
+            autoHideMenuBar: !!config.hide_menu,
             webPreferences: {
                 nodeIntegration: false,
-                sandbox: true,
+                sandbox: !!config.chromium_sandbox,
                 preload: PRELOAD_JS,
                 partition: partitionForAccount(account),
             },
@@ -131,6 +147,7 @@ function startNormalWindow(account: Account, config: Config): Promise<Window> {
         state.manage(win);
 
         win.webContents.on('dom-ready', () => {
+            applyUserCss(win, config);
             log.debug('Send config to renderer procress');
             win.webContents.send('mstdn:config', config, account);
         });
@@ -160,12 +177,12 @@ function startMenuBar(account: Account, config: Config, bar: Menubar.MenubarApp
             alwaysOnTop: IS_DEBUG || !!config.always_on_top,
             tooltip: 'Mstdn',
             useContentSize: true,
-            autoHideMenuBar: config.hide_menu,
+            autoHideMenuBar: !!config.hide_menu,
             show: false,
             showDockIcon: true,
             webPreferences: {
                 nodeIntegration: false,
-                sandbox: true,
+                sandbox: !!config.chromium_sandbox,
                 preload: PRELOAD_JS,
                 partition: partitionForAccount(account),
             },
@@ -176,6 +193,7 @@ function startMenuBar(account: Account, config: Config, bar: Menubar.MenubarApp
                 mb.window.webContents.openDevTools({mode: 'detach'});
             }
             mb.window.webContents.on('dom-ready', () => {
+                applyUserCss(mb.window, config);
                 log.debug('Send config to renderer procress');
                 mb.window.webContents.send('mstdn:config', config, account);
             });