This is going to be very hard to help with unless you can share some code that demonstrates what you have done so far. Otherwise a solution might not fit with the work you've already done. Specifically, how are you stylying the gray bar that is already there? What causes the ul > li > a > span structure that you are getting in that cell?
Best guess without actually being able to run this (it is very hard to debug a screenshot) is that you are using inline elements when you want to be using block elements. Another idea might be to assign a css class to the cell itself via the ColumnConfig's setColumnStyles or setColumnTextClassName. Beyond that, you need to provide more details, either here in the forums or privately in a real support ticket.