By default, form elements like input of type text and password (submit and button ?), select, textarea and button are styled with a monospace font with a resulting size of approx. 13.33px.
You can check C:\Program Files\Firefox\res\forms.css
(under WinXP) or with Firebug in the HTML part, the little triangle at the right of Style tab ==> Default CSS properties
body {
font: normal 62.5%/1.5 Verdana,Arial,Helvetica,sans-serif;
}
input, select, textarea, button {
font-size: 1.2em;
}
p {
font-size: 1.2em;
}
will result in 12px
+Verdana
form elements (and 1em = 10px
equivalence for your whole page)