Page uses available width better, no jumping margins

doc/gf-refman.html

@@ -15,7 +15,7 @@
     </style>
 </HEAD>
 <BODY>
-<div class="container my-5">
+<div class="container-fluid my-5" style="max-width:1200px">
 
 <P ALIGN="center">
     <CENTER>