em vs px… for mobile browsers

Question

For desktop browser all modern browser uses Zoom functionality so we can use PX but if same site can be seen on mobile then would px not be good for zooming in mobile browsers.

Answer 1

px won't be a real actual pixel when the screen is zoomed out on a modern mobile browser. These browsers are effectively emulating a desktop browser with desktop browser-size pixels.

So for this type of browser using px is no worse than it is for a normal desktop browser. You can do it if you want without major problems, but in both situations em is preferable for the main body content, if you can.