frappe/webnotes/templates/pages/404.html

{%- block title -%}Not Found{%- endblock -%}

{%- block header -%}
<h2 class="text-danger"><i class="icon-exclamation-sign"></i> Page missing or moved</h2>
{%- endblock -%}

{% block content %}
<div class="404-content">
	<div class="panel panel-default">
		<div class="panel-body">
			<p>We are very sorry for this, but the page you are looking for is missing
				(this could be because of a typo in the address) or moved.</p>
		</div>
	</div>
</div>
{% endblock %}