diff --git a/.gitignore b/.gitignore
index e795694..b23f2fe 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,5 +3,6 @@ src/db/config.php
 src/db/config-*
 src/config.php
 src/includes/vendor/
+src/content/theme/custom.css
 
 tests/
diff --git a/src/ext/CustomCSS/.htaccess b/src/ext/CustomCSS/.htaccess
new file mode 100644
index 0000000..8d2f256
--- /dev/null
+++ b/src/ext/CustomCSS/.htaccess
@@ -0,0 +1 @@
+deny from all
diff --git a/src/ext/CustomCSS/extension.json b/src/ext/CustomCSS/extension.json
new file mode 100644
index 0000000..64081e2
--- /dev/null
+++ b/src/ext/CustomCSS/extension.json
@@ -0,0 +1,6 @@
+{
+    "bundleId": "CustomCSS",
+    "name": "Custom CSS",
+    "version": "1.0",
+    "description": "Add you own css rules"
+}
diff --git a/src/ext/CustomCSS/lang/en.json b/src/ext/CustomCSS/lang/en.json
new file mode 100644
index 0000000..07adf87
--- /dev/null
+++ b/src/ext/CustomCSS/lang/en.json
@@ -0,0 +1,7 @@
+{
+    "ext.CustomCSS.name": "Custom CSS",
+    "customcss.h_css": "CSS",
+    "customcss.d_css": "Write you own CSS rules",
+    "customcss.not_writable": "CSS file is not writable, check permissions for custom.css",
+    "customcss.saved": "Saved"
+}
diff --git a/src/ext/CustomCSS/lang/ru.json b/src/ext/CustomCSS/lang/ru.json
new file mode 100644
index 0000000..90da2db
--- /dev/null
+++ b/src/ext/CustomCSS/lang/ru.json
@@ -0,0 +1,7 @@
+{
+    "ext.CustomCSS.name": "Дополнительные стили",
+    "customcss.h_css": "CSS",
+    "customcss.d_css": "Добавляйте собственные стили CSS",
+    "customcss.not_writable": "Ошибка записи в файл, проверьте права доступа к custom.css",
+    "customcss.saved": "Сохранено"
+}
diff --git a/src/ext/CustomCSS/loader.php b/src/ext/CustomCSS/loader.php
new file mode 100644
index 0000000..fa35437
--- /dev/null
+++ b/src/ext/CustomCSS/loader.php
@@ -0,0 +1,88 @@
+<?php declare(strict_types=1);
+
+/*
+    This file is a part of myTinyTodo.
+    (C) Copyright 2022 Max Pozdeev <maxpozdeev@gmail.com>
+    Licensed under the GNU GPL version 2 or any later. See file COPYRIGHT for details.
+*/
+
+if (!defined('MTTPATH')) {
+    die("Unexpected usage.");
+}
+
+function mtt_ext_customcss_instance(): MTTExtension
+{
+    return new CustomCssExtension();
+}
+
+class CustomCssExtension extends MTTExtension implements MTTExtensionSettingsInterface
+{
+    //the same as dir name
+    const bundleId = 'CustomCSS';
+
+    // settings domain
+    const domain = "ext.customcss.json";
+
+    const cssFilename = 'custom.css';
+
+    function init()
+    {
+        $prefs = self::preferences();
+        if (isset($prefs['css'])) {
+            $href = htmlspecialchars( get_unsafe_mttinfo('theme_url'). self::cssFilename. '?v='. ($prefs['edited'] ?? 0) );
+            $cb = function() use ($href) {
+                print "<link rel='stylesheet' type='text/css' href='$href'>\n";
+            };
+            add_action('theme_head_end', $cb);
+        }
+    }
+
+    function settingsPage(): string
+    {
+        $e = function($s) { return __($s, true); };
+        $prefs = self::preferences();
+        $css = htmlspecialchars($prefs['css'] ?? '');
+
+        return
+<<<EOD
+<div class="tr">
+ <div class="th"> {$e('customcss.h_css')}
+  <div class="descr">{$e('customcss.d_css')}</div>
+ </div>
+ <div class="td"> <textarea name="css" class="inmax monospace">$css</textarea> </div>
+</div>
+EOD;
+    }
+
+    function saveSettings(array $params, ?string &$outMessage): bool
+    {
+        if (defined('MTT_DEMO')) {
+            $outMessage = "Demo";
+            return true;
+        }
+        $css = $params['css'] ?? '';
+
+        $cssFilename = MTT_THEME_PATH. self::cssFilename;
+        if (!file_exists($cssFilename)) {
+            @touch($cssFilename);
+        }
+        if (!is_writable($cssFilename)) {
+            $outMessage = __('customcss.not_writable');
+            return false;
+        }
+        @file_put_contents($cssFilename, $css);
+        $outMessage = __('customcss.saved');
+        return true;
+    }
+
+    static function preferences(): array
+    {
+        $prefs['cssFilename'] = $cssFilename = MTT_THEME_PATH. self::cssFilename;
+        if (file_exists($prefs['cssFilename'])) {
+            $prefs['edited'] = filemtime($cssFilename) ?? 0;
+            $prefs['css'] = @file_get_contents($cssFilename) ?? '';
+        }
+        return $prefs;
+    }
+
+}