Note: After saving, you may have to bypass your browser's cache to see the changes. Mozilla / Firefox / Safari: hold down Shift while clicking Reload, or press Ctrl-Shift-R (Cmd-Shift-R on Apple Mac); IE: hold Ctrl while clicking Refresh, or press Ctrl-F5; Konqueror: simply click the Reload button, or press F5; Opera users may need to completely clear their cache in Tools→Preferences.

#wpTextbox1 {
  font-size: 13pt;
}