Hi Dianne,
You will need to add a font-size rule to the body selector in your CSS. Additionally, you should modify each other selector that has an explicit PX or PT for the font-size to use a relative sizing unit (% or EM).
Kyle Schaeffer has a very good article on font-size units and the PXtoEM.com website makes it easy to convert the units.
So, considering you want your base to be 16px, I would modify what you posted to look like this:
body
{
padding: 0;
margin:0;
color: #474747;
height:100%;
background-color: #71b8d9;
min-width: 1000px;
font-size: 100%; /* 100% = 1em = 16px = 12pt */
}
#art-main, table
{
font-family: Arial, "Helvetica", sans-serif;
font-size: 75%; /* 75% = 0.75em = 12px = 9pt */
}
HTH,
Joe D.