Center the calendar in the page:

.appContainer{text-align:center;}
.appContainer2{margin-left:auto;margin-right:auto;width:200px}

Change the calendar's width and height:

.yui-calendar td.calcell, #cp_abcform_pform .yui-calendar td.calcell {
padding-top:10px;
padding-bottom:10px;
border:1px solid #E0E0E0;
text-align:center;
vertical-align: top;
}

Change the background color of the selected date:

.yui-calendar td.calcell.reserveddate { background-color:#B6EA59; }

Make the calendar 100% width:

.yui-calendar td.calcell, #cp_abcform_pform .yui-calendar td.calcell {
border:1px solid #E0E0E0;
text-align:center;
vertical-align: top;
}
.yui-calendar .calheader, #cp_abcform_pform .yui-calendar .calheader {
width:100%;
}
.yui-calendar, #cp_abcform_pform .yui-calendar {
width:100%;
table-layout: fixed;
}

Other styles:

For other styles check the design section in the FAQ: https://abc.dwbooster.com/faq?page=faq#design

Customization / Edit Page

Sample Styles: