Responsive Landing Page using Flexbox

Another try at mobile-first design. I'm confused about the background image on this one. It looks okay at some sizes but when resizing the window the background image cuts off even with background-size: cover. I might have missed something. I also got in the habit of hiding the footer attributions on mobile view because with position: absolute and bottom: 0 it still floats up to the middle of the page at certain screen sizes.