making the background less cpu intensive

src/web/css/level2.css

@@ -12,6 +12,11 @@
 }
 html,
 body {
+  background:  no-repeat fixed;
+  -webkit-background-size: cover;
+  -moz-background-size: cover;
+  -o-background-size: cover;
+  background-size: cover;
   font-family: 'Patrick Hand SC', sans-serif;
   font-size: 18px;
   overflow-x: hidden;

src/web/js/level2.js

@@ -10,7 +10,6 @@ var t = new Trianglify(
     x_gradient: ["#d7191c","#fdae61","#ffffbf","#a6d96a","#1a9641"]
   }
 );
-var prevheight = height();
 
 window.onresize = function() {
     redraw();
@@ -19,7 +18,7 @@ window.onresize = function() {
 redraw();
 
 function redraw() {
-    var pattern = t.generate(document.body.clientWidth, height());
+    var pattern = t.generate(window.innerWidth, window.innerHeight);
     document.body.setAttribute('style', 'background-image: '+pattern.dataUrl);
 }