Website assets 'zoomed in' on desktop version, but not mobile - html

Question

I am using the following viewport meta in my html:
meta name="viewport" content="width=device-width, initial-scale=1
Which works perfectly for mobile devices. However, on the desktop version all assets, fonts and even the various elements are increased in size by 20%.
For example, see the image below. Even though the image is defined as being 300px by 300px in the devtools, if I take a screenshot and measure it in Photoshop it is in fact 360px by 360px.
The browser zoom is at 100%. What am I doing wrong?
/** EDIT **/
So, I found out that Windows sets the size of images and text to a default of 125%. That is why my website images and text were looking bigger. Now that I can see that is the case, how can I find a workaround so that even with the setting at 125% the images and text will display as intended? Is it even possible?

Answer 1

The problem is that a CSS px is not equal to a physical pixel. The definition is complicated, but in desktop browsers, the ratio between a CSS px and a physical pixel (A.K.A devicePixelRatio) is equal to the OS display scaling factor.
This is done in order to adapt to various screen resolutions and their distance to the observer. In my screen, the image in the codepen you sent is 600x600 physical pixels, because my screen is high PPI. I would have difficulty seeing text rendered with the default size in pixels.
If you really need to set the dimensions in physical pixels, you can just divide each dimension by `devicePixelRatio, but that creates accessibility concerns.

Answer 2

I worked it out in the end. In jQuery you can add the following to make your website display as intended:
$(document).ready(function(){
checkBrowserDpi();
}
function checkBrowserDpi(){
if(window.devicePixelRatio == 1.25 ) {
$("header, section, footer").removeClass("zoom100");
$("header, section, footer").addClass("zoom080");
} else {
$("header, section, footer").removeClass("zoom080");
$("header, section, footer").addClass("zoom100");
}
}
$(window).on('resize', function(){
checkBrowserDpi();
});
and then have two classes in your CSS file as follows:
.zoom100 { zoom: 100%; }
.zoom080 { zoom: 80%; }
In this particular case, it checks the device pixel ratio when the document is loaded and every time the window is resized and then sets the correct zoom to the header, section tags and footer for desktop browsers. You set the zoom to any tag you wish.
** EDIT **
As #D.Pardal points out this does create accessibility issues which I had not taken into consideration. That said, if you do want to mess with the devicePixelRatio then the method above works.