how to Change default fonts to Helvetica 16pix

Hi,
i need to have the fonts in the blog modified to “Helvetica 16pix”

here is the actual entry in my style.less.css
body { background: @htmlBgColor url(“{@htmlBg}”) @htmlBgRepeat @htmlBgX @htmlBgY @htmlBgAttach; color: @generalFontColor; line-height: 18px; width: 100%; min-width: 1000px; font-family: arial; font-size: 12px; }

can someone please post the change needed, and if making the change only there will be enough to get this result

thanks for your help
Halille