We often set the font-size of the HTML element to something like 10px, or 62.5%, because many people find it easier to work with factors of 10. Makes sense. There is a downside to this though. People are able to set a minimum font-size in their browser prefs. If your whole site and layout and all your mediaqueries, and all sizes are all based on ems, rems or percentages, this should be no problem at all. But if you use pixels for your mediaqueries, or if you need to set the width and height of a container in your carefully crafted layout in pixels, you do have an issue. You can test it with this page.