Update documentation

docs/graph2d.html

@@ -339,6 +339,12 @@ The options colored in green can also be used as options for the groups. All opt
   <td>'bottom'</td>
   <td>This determines if the shaded area is at the bottom or at the top of the curve. The options are 'bottom' or 'top'.</td>
 </tr>
+<tr>
+  <td class="greenField">shaded.style</td>
+  <td>String</td>
+  <td>undefined</td>
+  <td>Set the style for the shading. This is a css string and it will override the attributes set in the class.</td>
+</tr>
 <tr>
   <td class="greenField">style</td>
   <td>String</td>