--- style.css
+++ style.css
@@ -5064,6 +5064,9 @@ table.code-difftable .code pre {
     padding: 0;
     height: 17px;
     line-height: 17px;
+    tab-size: 4;
+    -moz-tab-size: 4; /* Code for Firefox */
+    -o-tab-size: 4; /* Code for Opera */
 }
 
 .add-bubble {
