code:
<!doctype html>
<html lang="hu">
<head>
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<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no" />
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href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css"
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<title>01-alerts</title>
</head>
<body>
CONTENT START
<h1>01-01-alerts simple</h1>
<h3>Simple</h3>
<div class="alert alert-primary" role="alert">
A simple primary alert—check it out!
</div>
<div class="alert alert-secondary" role="alert">
A simple secondary alert—check it out!
</div>
<div class="alert alert-success" role="alert">
A simple success alert—check it out!
</div>
<div class="alert alert-danger" role="alert">
A simple danger alert—check it out!
</div>
<div class="alert alert-warning" role="alert">
A simple warning alert—check it out!
</div>
<div class="alert alert-info" role="alert">
A simple info alert—check it out!
</div>
<div class="alert alert-light" role="alert">
A simple light alert—check it out!
</div>
<div class="alert alert-dark" role="alert">
A simple dark alert—check it out!
</div>
<hr />
CONTENT END
<h3 class="text-center">EoF</h3>
<hr />
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</body>
</html>