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<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" type="text/css" rel="stylesheet">
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<div class="alert alert-danger" role="alert">
<span class="input-group-text aria-hidden="true"></span>
<span class="sr-only">Error:</span>
Enter a valid email address
</div>
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<button type="button" class="btn btn-default navbar-btn">Sign in</button>