Animating the progress bar

src/sass/main.scss

@@ -317,9 +317,16 @@ header {
     background-size: rhythm(2) rhythm(2);
     background-repeat: repeat-x;
     height: 100%;
+
+    @include animation(progress 1.0s infinite linear);
   }
 }
 
+@include keyframes(progress) {
+  0% { background-position-x: rhythm(2); }
+  100% { background-position-x: 0; }
+}
+
 #error {
   background: $red;
   color: $white;