sr-only Bootstrap类
对除屏幕阅读器之外的所有设备都隐藏一个元素，该类只有.sr类。
您可以尝试运行以下代码以实现仅sr的Bootstrap-
示例
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap Example</title>
<link href = "/bootstrap/css/bootstrap.min.css" rel = "stylesheet">
<script src = "/scripts/jquery.min.js"></script>
<script src = "/bootstrap/js/bootstrap.min.js"></script>
</head>
<body>
<div class = "row" style = "padding: 91px 100px 19px 50px;">
<form class = "form-inline" role = "form">
<div class = "form-group">
<label class = "sr-only" for = "email">Email address</label>
<input type = "email" class = "form-control" placeholder = "Enter email">
</div>
<div class = "form-group">
<label class = "sr-only" for = "pass">Password</label>
<input type = "password" class = "form-control" placeholder = "Password">
</div>
</form>
</div>
</body>
</html>