user guide: put borders on body content

rb/assets/user_guide.html.erb

@@ -3,7 +3,27 @@
     <title>RScons User Guide - Version <%= Rscons::VERSION %></title>
     <style>
       body {
-        max-width: 140ex;
+        background-color: #CCC;
+        margin: 0px;
+        padding: 0px;
+      }
+      #body-table {
+        margin-left: auto;
+        margin-right: auto;
+        border-collapse: collapse;
+      }
+      #body-left-border {
+        width: 10px;
+        background-image: linear-gradient(to right, #CCC, #000, #FFF);
+      }
+      #body-right-border {
+        width: 10px;
+        background-image: linear-gradient(to right, #FFF, #000, #CCC);
+      }
+      #body-center {
+        background-color: #FFF;
+        max-width: 120ex;
+        padding: 1ex;
       }
       .code {
         padding-left: 2ex;
@@ -28,6 +48,12 @@
     </style>
   </head>
   <body>
-    <%= body %>
+    <table id="body-table">
+      <tr>
+        <td id="body-left-border"></td>
+        <td id="body-center"><%= content %></td>
+        <td id="body-right-border"></td>
+      </tr>
+    </table>
   </body>
 </html>