After a battle i found the solution "How to use CSS class inside a custom webpart page".
So to achieve this goal please follow the bellow steps,
1. Open the Solution File in Visual Studio (Webpart Page)
2. Do the changes in ChildControl Method
protected override
void CreateChildControls()
{
Control control =
Page.LoadControl(_ascxPath);
Controls.Add(control);
CssRegistration.Register("/Style%20Library/coreV5.css");
}
3. If you are creating a runtime table then use as below. In my case i have used this way:
writer.Write("<tr><td><table
width='100%' border='0' cellSpacing='0' cellPadding='0'><tr class='ms-WPHeader'><td
align='left' class='ms-wpTdSpace'></td><td
class='ms-WPHeaderTd'><h3 class='ms-standardheader ms-WPTitle'
style='text-align:justify;'><nobr><span>" +
productCategory + "
</span></nobr></h3></td><td align='right'
class='ms-WPHeaderTdMenu'></td><td
class='ms-WPHeaderTdSelection'></td><td align='left'
class='ms-wpTdSpace'></td></tr></table></td></tr>");