diff --git a/app/templates/base.html b/app/templates/base.html
index 29c8290..d972043 100644
--- a/app/templates/base.html
+++ b/app/templates/base.html
@@ -135,6 +135,13 @@
       });
     };
 
+    window.cassandraToggleTheme = function () {
+      var d = document.documentElement;
+      var t = d.dataset.theme === 'light' ? 'dark' : 'light';
+      d.dataset.theme = t;
+      try { localStorage.setItem('cassandra.theme', t); } catch (e) {}
+    };
+
     window.cassandraSetLang = async function (newLang) {
       var pill = document.getElementById('lang-toggle');
       if (!pill) return;
@@ -204,7 +211,7 @@
                 onclick="cassandraSetTone('INTERMEDIATE')">Intermediate</button>
       </div>
       <button class="theme-toggle" type="button" aria-label="Toggle theme"
-              onclick="(function(){var d=document.documentElement;var t=d.dataset.theme==='light'?'dark':'light';d.dataset.theme=t;try{localStorage.setItem('cassandra.theme',t);}catch(e){}})()">
+              onclick="cassandraToggleTheme()">
         <span class="theme-toggle__label"></span>
       </button>
       {% set cu = request.state.current_user if request.state and request.state.current_user is defined else None %}