How to make button disappear at certain screen sizes

Hi there, I made this temporary header that scrolls away when you move down the page past the image (when the real header drops down) but I don't want the buttons to appear when the browser size gets smaller than a certain size. I have custom css attached to the each button (using #bloc) to make them turn white on hover, so I probably just need to add more code to each one. Not sure! Any help would be appreciated. The site isn't live yet so I can't send a link.