> The browser might default to 16px font size, but users can pick something else. So if somebody had poor vision and increased their default font size; or if they had a small laptop screen and decreased their default font size, 1em * 62.5% != 10px, everything the designer set in ems was a different size than they intended, and a lot of their page layouts disintegrated into an unholy mess.
Howdy, author of the article you're responding to (but not the person who originally discovered/pioneered this trick). This is not true, and my article explains why.
The 62.5% trick is rarely used on its own, but people often cite it this way, leading to confusion. In practice, you set the root font size to 62.5% (of the user agent font size) and then also scale all body text back up to 1.6rem so it's not stuck at 10px. From here on out, all font sizes remain proportional no matter what, even if a user changes their preferred root font size in browser settings. Play around with the math if you doubt it (the article offers examples).
> everything the designer set in ems was a different size than they intended
That's working as intended—your design will scale up or down, according to the user's preferred font size. If you don't like this, your only option is to set font sizes in pixels, which [you shouldn't be doing anyway](https://www.aleksandrhovhannisyan.com/blog/use-rems-for-font...) (disclaimer: also written by me).
Howdy, author of the article you're responding to (but not the person who originally discovered/pioneered this trick). This is not true, and my article explains why.
The 62.5% trick is rarely used on its own, but people often cite it this way, leading to confusion. In practice, you set the root font size to 62.5% (of the user agent font size) and then also scale all body text back up to 1.6rem so it's not stuck at 10px. From here on out, all font sizes remain proportional no matter what, even if a user changes their preferred root font size in browser settings. Play around with the math if you doubt it (the article offers examples).
> everything the designer set in ems was a different size than they intended
That's working as intended—your design will scale up or down, according to the user's preferred font size. If you don't like this, your only option is to set font sizes in pixels, which [you shouldn't be doing anyway](https://www.aleksandrhovhannisyan.com/blog/use-rems-for-font...) (disclaimer: also written by me).