Same font size to all viewpoint

Dear Sir/Madam,

I can’t remember which veiwpoint I do first, now I find different viewpoint the font size are different, I want to force all viewpoint to a class with same font size 2.4rem. Please advise how I can do that.

In general practices, should I set the padding to container from sm viewpoint first or lg viewpoint first?

Best regards,

Kelvin