How to prevent gridview height with horizontal scrolbar resize depending on rows

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C#

ASP.NET

while applying page filters, depending on resultset(10 per page) my gridview height is shrinked. How do I avoid that and make gridview retain its height with horizontal scrollbar at same place even no. of rows is less than 10.

Pls help.

here is my code:

What I have tried:

<asp:GridView ID="gv_SOUpdate" runat="server" AllowPaging="true" ShowHeader="true"  
  AllowSorting="true"  style="border-color:Black;" 
  AutoGenerateColumns="False" BorderColor="White" GridLines="Both" PageSize="10"  
  BorderStyle="Solid"  width="1600px" 
 onpageindexchanging="gv_SOUpdate_PageIndexChanging"      
 onsorting="gv_SOUpdate_Sorting"
 BackColor="#CCCCCC"  
 onrowcreated="gv_SOUpdate_RowCreated" 
 onrowdatabound="gv_SOUpdate_RowDataBound"> 
 <HeaderStyle CssClass="GridviewScrollHeader"  ForeColor="black"/> 
 <RowStyle CssClass="GridviewScrollItem" /> 
  <PagerStyle CssClass="GridviewScrollPager" />


.GridviewScrollHeader TH, .GridviewScrollHeader TD 
{ 
  padding:4px;
font-weight: bold; 
border-right: 1px solid #AAAAAA; 
border-bottom: 1px solid #AAAAAA; 
background-color: #CCCCCC; 
text-align: center; 
vertical-align:middle;
font-family:Calibri;
border-color: Black;
z-index:0;} 

.GridviewScrollItem TD 
{ 
padding:4px;
border-right: 1px solid #AAAAAA; 
border-bottom: 1px solid #AAAAAA; 
background-color: #F1F2CD; 
font-family:Calibri;
border-color: Black;} 

.GridviewScrollPager  
 { 
border-top: 1px solid #303030; 
background-color: #FFFFFF; } 

.GridviewScrollPager TD 
{ 
padding-top: 3px; 
font-size: 14px; 
padding-left: 5px; 
padding-right: 5px; }

.GridviewScrollPager A 
{ 
color:Black;}
.GridviewScrollPager SPAN
{
font-size: 16px;
font-weight: bold;}