I have an issue with a Calendar Extender. It doesn't show all days because calendar is not big enough.

This is the calendar's code:
<asp:TextBox ID="txtStartDate" runat="server" MaxLength="10" /><ajaxToolkit:CalendarExtender ID="txtStartDate_CalendarExtender" runat="server"
PopupPosition="BottomRight" TargetControlID="txtStartDate"></ajaxToolkit:CalendarExtender>I tried to override calendar styles using CssClass property and adding a calendar css file on the application Theme, but WebResource is overriding all my changes.
I have this default skin:
<ajaxToolkit:CalendarExtender runat="server" CssClass="ajax__calendar" />
On client WebResource is always after theme styles:
<head><title>...</title>
...<link href="../App_Themes/Default/calendar.css" type="text/css" rel="stylesheet">
...<link href="/WebResource.axd?d=MCcdpl5IuwR6TANo95btJ6rXTHTnD-9oDJImhyXbzBmXZDMRe8JCPSohAosETiO8k0T7NiWj1iH3lVZwqTO7CHvq72AIseG4zJprbc72FFNI72fCq2HaLWSa2XakZk_5hi8ZltSfUK9q3d_R0stXvA2&t=634831691382171466" type="text/css" rel="stylesheet">
...</head>Do you have any idea of what is missing or wrong?