CSS: Is Helvetica the default 'sans-serif' font on Mac and Arial the default sans-serif font on Windows?

Question

I have a lot of CSS that does the following:

font-family: Helvetica, Arial, sans-serif;

It my understanding that Helvetica is the default sans-

Answer 1

With fonts, you want to be as specific as possible to prevent layout issues. Your page may look perfect on a machine with Arial as the default sans-serif font, but if someone has a very different font as their default, it can affect spacing of elements (if you use relative measures). Plus it makes any designer on the project angry when they see the wrong font, and you don't want that.