Sync css with blfs

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@11884 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

stylesheets/lfs-xsl/lfs.css

@@ -162,6 +162,8 @@ div.navheader, div.navfooter {
 
 div.navheader {
   border-bottom: 1px solid #dbddec;
+   position: sticky;
+   top: 0;
 }
 
 div.navfooter {