Fullscreen slider caption title and text font size in mobile mode

While the site goes in the mobile mode or is diplayed in a narrow window the font size set for caption title and caption text in fullscreen slider are reset. I would like to keep it like the firs line of the text was samller than the second so I have set the caption title font size smaller than the caption text size. I works while the site is displayed in wide window. In mobile mode, however the font size resets.

Is there a way to keep the text size proportion ?
Or, alternatively, is there a way to change the order of elements, just like in “special heading” settings?

Thanks in advance for the assistance.