Nativeness lies more in behavior than in looks. E.g. an input (an edit for old folks) has a very specific popup menu on every system, text selection works in a specific way (think what happens when you double/triple click, move with ctrl or lose or gain focus). Tab order and focusability is important as well. If they get that correctly, by e.g. using borderless system text areas or grabbing a menu from common control internals, it’s not a big deal if they draw some borders or animations by themselves. It’s just pixels in the end, sometimes better than native (which is just crap too often, like windows tables, lists, popdown controls).
But really, native look and feel only left on macOS. Windows lost its traditions around vista, linux never ever had one true way to do UI, and browsers almost exterminated everything else.
