Override 'Instruction for Users CSS' in form fields

I have found lots of complex CSS entries in the forum but non seem to answer my simple requirement. The CSS styling for the instructions below the form fields is silver - my site has a lot of older people accessing it so I would like to make these bolder by varying colour/font etc. Tried to do this in the entry box using html but this gave strange results. Any help would be good - thank you.

Hi,

Do you have Firebug ? it should help you find the class affecting the text in order to be able to override it.

Regards,
Max