<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>我是中国人</title>
<!-- 新 Bootstrap 核心 CSS 文件 -->
<link href="css/bootstrap.min.css" rel="stylesheet">
<!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
<script src="js/bootstrap.min.js"></script>
<script src="https://cdn.staticfile.org/popper.js/1.15.0/umd/popper.min.js"></script>
</head>
<body>
<div id="" class="container">
<label>用户名</label>
<input type="text" name="username" id="" value="" class="form-control" />
</div>
<div id="" class="container">
<label>邮箱</label>
<input type="email" name="email" id="" value="" class="form-control" />
</div>
<div id="" class="container">
<label>密码</label>
<input type="password" name="password" id="" value="" class="form-control" />
</div>
</body>
</html>
bootstrap输入框 
![龙珠训练营task04[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)