If a deeper level of customization is needed, there are widget-specific classes referenced within the jquery.ui.datepicker.css stylesheet that can be modified. These classes are highlighed in bold below.

Sample markup with jQuery UI CSS Framework classes

<div id="ui-datepicker-div" class="ui-datepicker ui-widget ui-widget-content ui-helper-clearfix ui-corner-all ui-helper-hidden-accessible">
   <div class="ui-datepicker-header ui-widget-header ui-helper-clearfix ui-corner-all">
      <a class="ui-datepicker-prev ui-corner-all">title="Prev"><span class="ui-icon ui-icon-circle-triangle-w">Prev</span></a>
      <a class="ui-datepicker-next ui-corner-all" title="Next"><span class="ui-icon ui-icon-circle-triangle-e">Next</span></a>
      <div class="ui-datepicker-title">
         <span class="ui-datepicker-month">January</span><span class="ui-datepicker-year">2009</span>
      </div>
   </div>
   <table class="ui-datepicker-calendar">
      <thead>
      <tr>
         <th class="ui-datepicker-week-end"><span title="Sunday">Su</span></th>
         ...
      </tr>
      </thead>
      <tbody><tr>
         <td class="ui-datepicker-week-end ui-datepicker-other-month "> 1 </td>
         ...
      </tr>
      </tbody>
   </table>
   <div class="ui-datepicker-buttonpane ui-widget-content">
      <button type="button" class="ui-datepicker-current ui-state-default ui-priority-secondary ui-corner-all">Today</button>
      <button type="button" class="ui-datepicker-close ui-state-default ui-priority-primary ui-corner-all">Done</button>
   </div>
</div>

Note: This is a sample of markup generated by the datepicker plugin, not markup you should use to create a datepicker. The only markup needed for that is <input type="text" /> or <div></div>.