function setMinWidth() {
     if (document.getElementById('header').offsetWidth <= 840) {
       document.getElementById('headerImage').style.right = "";
       document.getElementById('headerImage').style.left = "453px";
       document.getElementById('mainNav').style.width = "840px";
     } else {
       document.getElementById('headerImage').style.right = "0px";
       document.getElementById('headerImage').style.left = "";
       document.getElementById('mainNav').style.width = "100%";
     }
   }
   window.onresize = function() {
     setMinWidth();
   }
   window.onload = function() {
     setMinWidth();
   }