is there anyway that I can set different size of background
so that it appears according to the user's resolution setting?

For example, is it possible to have one background for 1920x1080, one for 1600x1200 and 1377 and 788 and etc?

Dear taewoo no,

Where do you want to change background? You can go to file templates/sj_perty/css/responsive.css, add add background to class of elements following your idea in: @media (min-width: 767px) and (max-width: 979px) , @media (max-width: 767px), @media (max-width: 480px) , @media (max-width: 360px) , @media (max-width: 320px), @media (min-width: 1200px)

Thanks