How to set some items of an Ajax Toolkit ComboBox to bold or to a different color?

How to set some items of an Ajax Toolkit ComboBox to bold or to a different color?

We want to emphasize the top about 10 items (number varies based on other criteria) in bold or perhaps a lightgray background. The Ajax Toolkit ComboBox is filled from an SQL database. After it is filled (or perhaps while it is being filled) we'd like to bold the top so many items. How to do this in JQuery?