diff --git a/themes/original/css/common.css.php b/themes/original/css/common.css.php
index 4ff4130370..f2821b6a18 100644
--- a/themes/original/css/common.css.php
+++ b/themes/original/css/common.css.php
@@ -401,6 +401,8 @@ img.lightbulb {
     image-rendering: pixelated;
     vertical-align:     middle;
     margin-<?php echo $left; ?>:        0.3em;
+    background-repeat: no-repeat;
+    background-position: center;
 }
 
 /* no extra space in table cells */