title: Python Flask flash not working correctly
body: <p>I've simple 2 line code :</p>
  
  <pre><code>@app.route('/contact/')
  def contact():
    flash('We are reachable at ')
    return render_template('contact.html')
  </code></pre>
  
  <p>I get the message 'We are reachable at' at /contact but it appears are normal text message. It doesn't background color(blue) or disappears after seconds. 
  where contact.html contains</p>
  
  <pre><code>{% extends "layout.html" %}
  
  {% block title %}Contact{% endblock title %}
  
  {% block body %}
    &lt;h2&gt; Contact Us  &lt;/h2&gt;
     Your email address must be valid as this is where reply
     will be sent. We do not share this address with anybody.
  
  {% endblock body %}
  </code></pre>