Text size different after upgrade

After updating my testserver to CB 2.3.0+build.2018.11.26.18.02.53.89a6e2ebd
all text in both backend and frontend were changed,
in backend Went bigger and all text in frontend Went smaller.

Unfortunately, I updated Joomla to 3.9.1 before I noticed this.

Before starting all over to find the reason, is this a common issue?
And hopefully, there is a simple solution.

Using JA T3 framework and default CB template with minor color changes in a custom CB template.
In backend Everything is default.

See the below regarding font size.

www.joomlapolis.com/forum/6-news-and-publicity/239316-community-builder-2-2-bootstrap-4-release?start=6#305472

A lot of templates change the root font size, which they absolutely should not be doing. "em" inherited font size should be on the body element and not the html element. Setting it on html element breaks what font size "rem" inherits from, which should be the persons device set font size for accessibility.

Thanks! We will investigate the template.
Obviously, Joomla default backend template acts as you describe as well.

Default Joomla isis backend template does not behave that way. They set a font size of 100%, which is fine as that inherits from device (setting to 100% or inherit are both acceptable means of resetting). If it's doing this in backend then you've likely something installed loading CSS that's setting the font size on the html root element.