Body size is set to 14px

Starting from Jira 8.12 the font size is set to 14px. Before it used to be set to 16px or unset. This is breaking our app designs since we rely on the relative ems (rem) to make the interface render nicely on all screens. The size of one rem is calculated based on the size of the font size of the body element.

What is the reasoning behind changing this?

We have also seen it being introduced in Bitbucket Cloud. Is this something that is being introduced across all platforms?