Multidevices resolution

Hey !

I am planning to make a game to be played on computer, smartphone and tablet.
How can I manage to fit different resolution with a single project ?

Is it better to stick on computer ratio (1920 x 1080) and then just center it on a smartphone (2400 x 1080) ? In landscape height will be the same, there will be 2 empty area on the left and right.

Thanks a lot !