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To make your header responsive, you can utilize PRO Header visibility settings.
Add another ROW with exact same content but make your columns stack instead of inline.
Then make your original ROW to be visible only on desktop and the new ROW to be visible only in mobile.
I went ahead and added the row to give you an example.
You will be able to see it in action by clicking on this mobile icon and clicking on screen size on top
Hope that helps