<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<!doctype html>
<HTML lang="pt-br">
<head>
<meta charset="utf-8">
<title>Formas Geométricas </title>
</head>
<body>
<form class="form-horizontal">
<fieldset>
<legend>Formas Geométricas</legend>
<h4>Quadrado:</h4>
<div class="form-group">
<label class="col-md-1 control-label" for="textinput">Lado</label>
<div class="col-md-2">
<input id="textinput" name="textinput" type="text" placeholder="" class="form-control input-md">
</div>
</div>
<h4>Retângulo:</h4>
<div class="form-group">
<label class="col-md-1 control-label" for="textinput">Base</label>
<div class="col-md-2">
<input id="textinput" name="textinput" type="text" placeholder="" class="form-control input-md">
</div>