You can make a custom skin, based on the Web20 skin, following these guidelines:
In order to make the calendar smaller, you will need to modify/remove the following Web20 style
/* all links in the calendar */
.TableLayout_Web20 td a
There are a couple of more styles like these to be removed, for example for the .DaysOfWeek_Web20
In addition, you may want to decrease all font-sizes.
Let us know if you need further assistance.
the Telerik team