Change .ltx_page_main max-width to 80em

The em unit seems like a more appropriate for the width of a text.

css/LaTeXML-navbar-left.css

@@ -35,7 +35,7 @@
   position: absolute;
   left: 350px;
   top: 0px;
-  max-width: 30cm;
+  max-width: 80em;
   padding: 0em 1em;
   background: white; /* Avoid strange effect when scrolling horizontally causing overlap with navbar. */
 }