diff --git a/BookReaderDemo/BookReaderDemo.css b/BookReaderDemo/BookReaderDemo.css
index 6d60573e3..57ba1e7e0 100644
--- a/BookReaderDemo/BookReaderDemo.css
+++ b/BookReaderDemo/BookReaderDemo.css
@@ -32,7 +32,10 @@ ia-bookreader{
 }
 
 .BookReader {
+    --br-height: calc(100vh - 100px);
+    --new-height: calc(var(--br-height) - 20px); 
     height: var(--br-height);
     overflow: hidden;
     margin: 0 auto;
 }
+