tables and styles

Hello,

I am having problems with using styles inside table-tags. The style
definitions are located in external stylesheets. For example, I have
defined a .headline style which I use with a '<H3>' tag. One of the
attributes of .headline is 'FONT-FAMILY:sans-serif;'. This works fine,
but when I use it inside a table ( <TD><H3
CLASS="headline">text</H3></TD> ) the font is depicted as a serif font.
There are many other examples of variable behaviour with different
elements inside tables.
Can somebody please give me a few tips or direct me to an information
source specifically about using styles in tables?

thanks in advance
simon