Hello i got this problem i got website that on 100% zoom looks normal but when i zoom to 110% + borders starts act weird way. On some of the borders thickness is rendered 2x
following up what @pepo_rasta said about pixels i would recommend not using them at all. I would recommend em or some other relative unity to do your borders in for scaleability
have a look at this
ems v px
its because of browser, when usinng zoom in browser it will only render how it would look like at choosen zoom level, so if you have 1px border at 110% its 1.1px border. Since you cant show only part of a pixel, it will show either 1px or 2px