Hi Mikael,
Please see the following sample:
<%@ Page Language="C#" %>
<%@ Register Assembly="Coolite.Ext.Web" Namespace="Coolite.Ext.Web" TagPrefix="ext" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title></title>
<script runat="server">
protected void Click(object sender, AjaxEventArgs e)
{
System.Threading.Thread.Sleep(1500);
}
</script>
<style type="text/css">
.red .ux-mselect
{
background-color: Red !important;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<ext:ScriptManager ID="ScriptManager1" runat="server" />
<ext:MultiSelect ID="MultiSelect1" runat="server" Width="300" Height="250">
<Items>
<ext:ListItem Text="Item 1" Value="1" />
<ext:ListItem Text="Item 2" Value="2" />
<ext:ListItem Text="Item 3" Value="3" />
<ext:ListItem Text="Item 4" Value="4" />
<ext:ListItem Text="Item 5" Value="5" />
</Items>
</ext:MultiSelect>
<ext:Button runat="server" Text="Ajax event">
<AjaxEvents>
<Click OnEvent="Click"
Before="#{MultiSelect1}.addClass('red');"
Success="#{MultiSelect1}.removeClass('red');"
Failure="#{MultiSelect1}.removeClass('red');">
</Click>
</AjaxEvents>
</ext:Button>
</form>
</body>
</html>