How do I change the font size?

Ide like to change the

font size, because the standard font size for text with bluemaster is quite small. Ive gone into style.css and this is all I can find for

:

p { margin:0 0 10px 0; }

I changed this to p { margin:0 0 10px 0; font-size:20px; } but this doesn't change the font size.

Thanks