<asp:GridView> width, <div> width

Answer 1

The border of the grid (which is a table) is outside the 100% width (this is the way standards mode CSS works). Also the center tag is depreciated in standards mode.

A trick you could use to fix this problem is to rewrite the inner div tag to be a table like the grid:

<table style="border-top: Solid 1px Black; border-left: Solid 1px Black; 
  border-right: Solid 1px Black; border-collapse:collapse; 
  background-color: #EEEEEE; width:100%">
  <tr>
    <td style='padding: 5px'>(inner stuff)</td>
  </tr>
</table>

That way it will have the same identical border outside the table.