CSS problem in visual format editor

Jaman

We have customized the css in VFE for our client. Currently, there are 5 styles by which the user can select to change the content. Initially, it works well when user selects any style for any wording, but after a style has been selected, we can not change this style to another even if we highlight it and select different style. Could any body help to tell me how to fix it. Thanks!