How do i approach the design like jira website does?

Question

I have a react project that is really complex design and like jira project management page
#1 -> How to do the design is same for all devices (all viewports) like jira does

Answer 1

use relative units in all your css dimension, and think to your design to be able to fit in all kind of dimensions and width/height ratios (both portrait and landscape modes...)

but there's no magic: if your design is complex, making it same for all devices will be complex to achieve (it's even not simple to do it for less complex design) ^^

however, making it "really" responsive (ie: design change based on dimensions / ratios) will simplify a bit the process... but it would remain quite complex ;P