To be fair, let's not pretend we haven't all written JS to resize shit in desperation when the CSS doesn't work. Though the better way to do this would probably be to listen for the window size change to fire your style changing functions. That makes it behave more like responsive CSS that changes automatically when you resize the window (though with a slight lag sometimes because it's a lot more computationally expensive). Though it could also be due to the browser putting unused tabs to sleep and stopping JS execution which would be outside the website's control.