"Currently there is no opinionated way to construct responsive layouts in Evergreen. In the case of responsive layouts you might want to simply use a div with a class name and use breakpoints in CSS — or potentially a CSS-in-JS solution."
It's responding to the device and the ways the user will interact with it. For example, the combobox example in Evergreen doesn't actually use a <select> in the background, so users on mobile devices will actually have to use the dropdown implementation rather than the browser displaying a proper native mobile select. That's a much worse experience. Not to mention Evergreen will be completely inaccessible for users who need assistive technology, which potentially poses legal issues...
It's responding to the device and the ways the user will interact with it. For example, the combobox example in Evergreen doesn't actually use a <select> in the background, so users on mobile devices will actually have to use the dropdown implementation rather than the browser displaying a proper native mobile select. That's a much worse experience. Not to mention Evergreen will be completely inaccessible for users who need assistive technology, which potentially poses legal issues...