Here's a handy list of CSS font stacks for Windows & macOS browsers. Adapted from coderwall.com/p/57imrw/common-fonts-for-windows-mac
The first CSS stack on this list can just be reduced down to just Sans-Serif as Windows browsers will get Arial & macOS browsers get Helvetica.
Click on the sample text to edit!

<p style="font-family: Arial, Helvetica, Sans-Serif">

<p style="font-family: Arial Black, Gadget, Sans-Serif">

<p style="font-family: Comic Sans MS, Textile, Cursive">

<p style="font-family: Courier New, Courier, Monospace">

<p style="font-family: Georgia, Times New Roman, Times, Serif">

<p style="font-family: Impact, Charcoal, Sans-Serif">

<p style="font-family: Lucida Console, Monaco, Monospace">

<p style="font-family: Lucida Sans Unicode, Lucida Grande, Sans-Serif">

<p style="font-family: Palatino Linotype, Book Antiqua, Palatino, Serif">

<p style="font-family: Tahoma, Geneva, Sans-Serif">

<p style="font-family: Times New Roman, Times, Serif">

<p style="font-family: Trebuchet MS, Helvetica, Sans-Serif">

<p style="font-family: Verdana, Geneva, Sans-Serif">

<p style="font-family: MS Sans Serif, Geneva, Sans-Serif">

<p style="font-family: MS Serif, New York, Serif">