<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>bootstrap表单的基本操作</title>
<link rel="stylesheet" href="css/bootstrap.min.css">
<script src="js/jquery-3.3.1.min.js"></script>
<script src="js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<div class="row">
<div class="col-md-12">
<form action="" role="form">
<fieldset>
<legend>用户登陆</legend>
<div class="form-group">
<label for="name">用户名登陆：</label>
<input type="text" class="form-control" id="name" placeholder="UserName">
<p class="help-block">可以用手机号和邮箱登陆</p>
</div>
<div class="form-group">
<label for="password">密码：</label>
<input type="text" class="form-control" id="password" placeholder="PassWord">
<p class="help-block">密码不得少于6位</p>
</div>
</fieldset>
<button type="submit" name="button" class="btn btn-info btn-block">提交</button>
</form>
</div>
</div>
</div>
</body>
</html>
其他的请参考：https://v3.bootcss.com/css/#forms
<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>bootstrap表单自适用设计</title>
<link rel="stylesheet" href="css/bootstrap.min.css">
<script src="js/jquery-3.3.1.min.js"></script>
<script src="js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<form action="" role="form" class="form-horizontal">
<fieldset>
<legend class="text-center">用户登陆</legend>
<div class="form-group">
<label for="name" class="col-md-2 control-label">用户名登陆：</label>
<div class="col-md-10">
<input type="text" class="form-control" id="name" placeholder="UserName">
</div>
</div>
<div class="form-group">
<label for="password" class="col-md-2 control-label">密码：</label>
<div class="col-md-10">
<input type="text" class="form-control" id="password" placeholder="PassWord">
</div>
</div>
</fieldset>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<button type="submit" name="button" class="btn btn-info">提交</button>
</div>
</div>
</form>
</div>
</body>
</html>