line-height:12pt; height:10px;
"px" in css doesn't correspond to literal pixels on the display.
>By definition, this is the physical size of a single pixel at a pixel density of 96 DPI, located an arm's length away from the viewer's eyes.
The only reason why they're in pt is that who wrote the stylesheet didn't know any better.
1: https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_...
It's not device independent like "pt", it's not what most people expect it to be (one device pixel), and there's subjective "wiggle room" in what it actually means.
People are different, so it's good to have font size and zoom options. Some can go bigger, some can go smaller. I use 80% on a lot of sites, and an extension called 'Zoom Page WE' to remember the settings.