FormViewGridView.aspx font size:
C# source: FormViewGridView.aspx   fetchData_sql.cs   
View Sample
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>

<html>
<head>
<title>FormView with Nested GridView</title>
<link rel="stylesheet" href="/shared/netdemos.css">

<script language="C#" runat="server">
   void getImageUrl ( Object src, EventArgs e ) {
      DataRowView dataRow = ( DataRowView ) categoriesFormView.DataItem;
      string catName = dataRow [ "CategoryName" ].ToString ( ).Replace ( "/", " " );
      Image img = ( Image ) categoriesFormView.FindControl ( "img" );
      img.ImageUrl = string.Format ( "/shared/images/nwind/{0}.png", catName );
   }
</script>
</head>

<body>
<!-- #include virtual="~/shared/top.inc" -->
<div class="header"><h2>FormView with Nested GridView</h2></div>

<hr size=1 width=92%>

<form runat="server">
<div align="center">

   <asp:formview id="categoriesFormView" runat="server"
      datasourceid="categories"
      datakeynames="categoryid"
      width=90% cellpadding=5
      gridlines="both"
      allowpaging
      ondatabound="getImageUrl">

      <headerstyle backcolor="darkslategray" forecolor="khaki" 
         height="18pt" font-bold />

      <rowstyle backcolor="ghostwhite" font-size="9pt" 
         verticalalign="top" />

      <pagersettings
         mode="nextprevious"
         nextpagetext="Next" previouspagetext="Back" />

      <pagerstyle horizontalalign="right" />

      <headertemplate>
         Northwind Traders Products Inventory</span>
      </headertemplate>

      <itemtemplate>
         <table width=100% cellpadding=5>
         <tr align="center">
            <td>
               <asp:image id="img" runat="server" />
               <div id="msg"><%# Eval ( "CategoryName" ) %></div></td>

            <td>
               <asp:gridview id="categoryDetailsGrid" runat="server"
                  datasourceid="categoryInfo"
                  width=96% font-size="10pt" cellpadding=5
                  gridlines="horizontal" autogeneratecolumns=false>

                  <headerstyle height="18pt" font-bold
                     backcolor="steelblue" 
                     forecolor="mintcream"
                     horizontalalign="center" />

                  <rowstyle backcolor="whitesmoke" verticalalign="top" />

                  <columns>
                     <asp:boundfield headertext="Product"
                        datafield="productname" />
                     <asp:boundfield headertext="Packaging"
                        datafield="quantityperunit" />
                     <asp:boundfield headertext="In Stock"
                        datafield="unitsinstock"
                        itemstyle-horizontalalign="right"/>
                     <asp:boundfield headertext="Unit Price"
                        datafield="unitprice" 
                        htmlencode=false
                        dataformatstring="{0:c}" 
                        itemstyle-horizontalalign="right"/>
                  </columns>
               </asp:gridview>
            </td></tr>
         </table>
      </itemtemplate>

   </asp:formview>

   <asp:sqldatasource id="categories" runat="server"
      selectcommand = "SELECT * FROM Categories"
      connectionstring="<%$ ConnectionStrings:aspnet %>" />

   <asp:sqldatasource id="categoryInfo" runat="server"
      selectcommand = "SELECT * FROM Products WHERE CategoryId = @CategoryId"
      connectionstring="<%$ ConnectionStrings:aspnet %>">
      <selectparameters>
         <asp:controlparameter name="CategoryId" controlid="categoriesFormView"
            propertyname="selectedvalue" />
      </selectparameters>
   </asp:sqldatasource>

</div>
</form>

<hr size=1 width=92%>
<!-- #include virtual="~/shared/viewsrc.inc" -->

</body>
</html>