diff --git a/share/base.css.in b/share/base.css.in
index 06e9408..dac352e 100644
--- a/share/base.css.in
+++ b/share/base.css.in
@@ -16,7 +16,7 @@
   overflow:auto;
 }
 #page-container { /* PDF container */
-  position:absolute;
+  position:absolute; /* required for calulating relative positions of pages in pdf2htmlEX.js */
   top:0;
   left:0px;
   margin:0;