In Sharepoint or your custom web applications you want to change cascading style sheet (css)dynamically. In this case you can use javascript to do this. Christopher Heng describes this inthesitewizard.com 

TABLE.ms-recyclebin TD {
     background: #000000 url('<image_path>') repeat-x;
     border: 1px solid #FFFFFF;
} 

TABLE.ms-recyclebin TD A{
     color: #FFFFFF;
}

SPSite  _site =  new   SPSite ( " http://portal " );
SPWeb web = _site.AllWebs[0];
Microsoft.SharePoint.SPList list = web.SiteUserInfoList;
Microsoft.SharePoint.SPUser user = web.SiteUsers["DOMAIN\\portal.user1"];
Microsoft.SharePoint.SPListItem item = list.Items.GetItemById(user.ID);
item["Picture"] ="http://portal/SiteCollectionImages/portaluser1.jpg";
item.Update();

listsWS. Lists   listService = new listsWS. Lists() ;
listService.Url =  "http://litwareportal/<your_site>/_vti_bin/lists.asmx" ;
listService.Credentials =  new  System.Net.NetworkCredential( "Administrator" ,  "Pa$$w0rd" , "LITWAREINC" );

XmlDocument   doc =  new   XmlDocument () ;
XmlNode   viewFieldsParent = doc.CreateElement( "ViewFields" );
viewFieldsParent.InnerXml =
"<FieldRef Name=\"Author\"/>" +
"<FieldRef Name=\"BookName\"/>" +
"<FieldRef Name=\"PageCount\"/>";

XmlNode listItems = listService.GetListItems( "Books" ,  "" , null, viewFieldsParent,  "0" , null,  "" );

foreach  ( XmlNode   item  in  listItems.SelectNodes( "//*[local-name()='row']" ))
{
Console .WriteLine( "Author: "  + item.Attributes.GetNamedItem( "ows_Author" ).Value);
Console .WriteLine( "Book Name: "  + item.Attributes.GetNamedItem( "ows_BookName" ).Value);
Console .WriteLine( "Page Count: "  + item.Attributes.GetNamedItem( "ows_PageCount" ).Value);
Console .WriteLine( "#####################################" );
}

Console .ReadLine();