diff --git a/categories.js b/categories.js
index 06e876f..ead8d16 100644
--- a/categories.js
+++ b/categories.js
@@ -4,9 +4,19 @@ var form = document.getElementById("form-categories");
 
 for(var i = 0; i < categories.length; ++i)
 {
-    categories[i].addEventListener('change', function() {
+    categories[i].addEventListener('change', function(event) {
         'use strict';
-        form.submit();
+        var cat_id = event.target.id.replace('cat_','');
+
+        var events = document.getElementsByClassName('event_in_cat_'+cat_id);
+
+        for(var i = 0; i < events.length; ++i)
+        {
+            var evt = events[i];
+            evt.className = evt.className.replace(' bad_cat','');
+            if(event.target.checked == false)
+                evt.className += ' bad_cat';
+        }
     }, false);
 }