diff --git a/app/config/routes.ini b/app/config/routes.ini
index 0b250d4..992c0e0 100644
--- a/app/config/routes.ini
+++ b/app/config/routes.ini
@@ -46,6 +46,9 @@ POST /tag/create=TagController->create
 ; parsedown preview
 POST /parsedown/preview=ParsedownPreview->view
 
+; toggle-theme
+POST /toggle-theme = ThemeController->toggle
+
 ; dashboard
 GET /dashboard=DashboardController->index
 
diff --git a/app/controllers/ThemeController.php b/app/controllers/ThemeController.php
new file mode 100644
index 0000000..81beeb8
--- /dev/null
+++ b/app/controllers/ThemeController.php
@@ -0,0 +1,13 @@
+<?php
+
+class ThemeController
+{
+    function toggle($f3)
+    {
+        $current = $f3->get('SESSION.theme') ?: 'light';
+        $new_theme = ($current === 'light') ? 'dark' : 'light';
+        $f3->set('SESSION.theme', $new_theme);
+
+        $f3->reroute($f3->get('HEADERS.Referer') ?: '/');
+    }
+}
\ No newline at end of file
diff --git a/ui/templates/layout.html b/ui/templates/layout.html
index 65d6ccf..0a06759 100644
--- a/ui/templates/layout.html
+++ b/ui/templates/layout.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<html lang="en">
+<html data-theme="{{ @SESSION.theme ?? 'light' }}" lang="en">
 
 <head>
   <meta charset="UTF-8">
@@ -52,6 +52,13 @@
       <div class="navbar-end">
         <div class="navbar-item">
           <div class="buttons">
+            <form id="theme-toggle-form" method="post" action="/toggle-theme" style="display:inline">
+              <button type="submit" id="theme-toggle-button" class="button is-small" aria-label="Toggle Theme">
+                <span class="icon">
+                <i class="fas fa-circle-half-stroke" id="theme-icon"></i>
+                </span>
+              </button>
+            </form>
             <check if="{{ isset(@SESSION.user) }}">
               <true>
                 <a class="button is-primary" href="/logout">Log Out</a>
