Thanks, it’s an interesting discussion 
I could change the font-weight but that would then get bolder for other platforms.
On the typography page https://vaadin.com/docs/latest/styling/lumo/lumo-style-properties/typography it says that Arial and Helvetica are chosen for ‘other’ platforms, but neither of those fonts are out of the box installed on most Linux distros. Anyway, i will leave it as it is. At least i am aware of such rendering issues and if users complain will know where to look. Many thanks for your thoughts !