I noticed that we have a `.toolbarButton.group` CSS class, which is currently applied to some buttons in the viewer. Since it attempts to adjust the `margin-right` property, I was initially a bit puzzled as to why there wasn't different rules for LTR/RTL locales.
However, checking the viewer with the DevTools inspector, in both LTR and RTL locales, I quickly found that the rule in question is *always* being overridden by other CSS rules.
It thus seem to me that while this rule was probably useful at some point, it has been dead for years and could now be removed.