title: Unable to set property 'onclick' of undefined or null reference
body: <p>I made new project in Visual Studio 2015. It's JavaScript Windows App. I'm trying to make "Hello" application, but when i want compile it i get this error: </p>
  
  <blockquote>
    <p>0x800a138f - JavaScript runtime error: Unable to set property 'onclick' of undefined or null reference</p>
  </blockquote>
  
  <p>My code: </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>document.getElementById("button").onclick = function () {
      var jmeno = document.getElementById("Jmeno").value
      var pop = new Windows.UI.Popups.MessageDialog("&lt;%=Ahoj.Clientid%&gt;" + jmeno);
      pop.showAsync()
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
      &lt;meta charset="utf-8" /&gt;
      &lt;title&gt;App1&lt;/title&gt;
  
      &lt;!-- WinJS references --&gt;
      &lt;link href="WinJS/css/ui-dark.css" rel="stylesheet" /&gt;
      &lt;script src="WinJS/js/base.js"&gt;&lt;/script&gt;
      &lt;script src="WinJS/js/ui.js&gt;&lt;/script&gt;
  
      &lt;!-- App1 references --&gt;
      &lt;link href="/css/default.css" rel="stylesheet" /&gt;
      &lt;script src="/js/default.js"&gt;&lt;/script&gt;
      &lt;script src="js/zdravic.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body class="win-type-body"&gt;
      &lt;header&gt;
          &lt;h1&gt;Hello user! :)&lt;/h1&gt;
      &lt;/header&gt;
      &lt;section&gt;
          &lt;input id='Jmeno' type="text" placeholder="Zadej své jméno"/&gt;
          &lt;button id="button"&gt;Klikni na mě!&lt;/button&gt;
      &lt;/section&gt;
  &lt;/body&gt;
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>And for more, default.css doesn't work for me. Like it wouldn't be there. And yes, i have link it there.</p>