Font reset making text small in block editor

I've just updated all plugins and GP theme and WP to 6.1

Now the text in block editor is tiny, it's being rendered at around 8px.

I use the 62.5% and 1.6rem sizing to reset font size and make 3rem = 30px, and so on

It's worked fine for ages, but now breaks in wp6.1

as detailed here
https://www.aleksandrhovhannisyan.com/blog/62-5-percent-font-size-trick/#respecting-a-users-font-size-preferences

eg
html {
/* 10px */
font-size: 62.5%;
}

body {
/* 16px */
font-size: 1.6rem;
}

This is done in the GP typography section, setting HTML size to 62.5% and BODY 1.6rem .But now this isnt working as it looks like I need to put a base of 16px on somewhere as well. Usually this is implied in the browser, but WP seems to overriding this.

Can you help me work out how to get this to work in GP please? It was all working fine before wp6.1

Thanks
Ben