css - Tablesorter jQuery plugin width of column -

i use jquery plugin tablesorter. columns have same width. change width of first column via css, there no change.

i tried add widthfixed: false:

$("#activitiestable").tablesorter(         { widthfixed: false }         ); 

still there no change in column's width.

how can change column's width in table, when using tablesorter?

thanks