The default icon of the Date-Picker in the Extension Library from OpenNTF is nice but not sexy. You can change it to one of the cool "Font Awesome Icons".

First, add a DatePicker component to your page:

<xe:djDateTextBox id="datePickerComp" value="#{myDoc.myDateField}" />

Then add these lines to your custom CSS file:

/*
   ---------------------------------------------------- 
   Improve xe:djDateTextBox Elements with another icon.
   ---------------------------------------------------- 
*/

.dijitSelect .dijitArrowButton{
    padding:0px;
}

/* hide default arrow icon: */
.dijitDateTextBox .dijitArrowButtonInner{
    display: none;
}

.dijitDateTextBox .dijitArrowButtonContainer:after{
    font: 12px/normal FontAwesome; 
    content: "\f073"; /* <--- unicode of the icon */
    font-size-adjust: none; 
    font-stretch: normal;
}
/* ---------------------------------------------------- */

The value of attribute content is the "Icon-Code" (in this example "\f073" is the simple "fa-calendar" icon).

If you want another icon, visit http://fontawesome.io/icons/, search for your favorite icon, click to open ist detail, and there copy the Unicode. Paste the Unicode into yout custom CSS file as value of attribute content.