added background image

app/templates/activeBackground/activeBackground.css

@@ -0,0 +1,11 @@
+.background {
+  position: absolute;
+  left: 0;
+  top: 0;
+  height: 100%;
+  z-index: -1;
+}
+
+.background > img {
+  height: 100%;
+}

app/templates/activeBackground/index.js

@@ -0,0 +1,10 @@
+const html = require('choo/html');
+const assets = require('../../../common/assets');
+
+module.exports = function() {
+  const backgrounds = assets.match(/background/);
+  const src = backgrounds[Math.floor(Math.random() * backgrounds.length)];
+  return html`<div class="background">
+    <img src="${src}">
+  </div>`;
+};