diff --git a/src/web_interface/static/css/line_numbering.css b/src/web_interface/static/css/line_numbering.css
index a830a68ce..818d0b358 100644
--- a/src/web_interface/static/css/line_numbering.css
+++ b/src/web_interface/static/css/line_numbering.css
@@ -5,10 +5,10 @@
 
 #preview-div pre .line-number {
   float:left;
-  margin: 0;
   border-right:1px solid;
   text-align:right;
-  margin-right: 1em;
+  margin: 0 1em 0 0;
+  user-select: none;
 }
 
 #preview-div pre .line-number span {