<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<script type="text/javascript" src="js/jquery-3.3.1.js"></script>
<style type="text/css">
.fileinput-button {
position: relative;
display: inline-block;
overflow: hidden;
}
.fileinput-button input{
position:absolute;
right: 0px;
top: 0px;
opacity: 0;
-ms-filter: 'alpha(opacity=0)';
font-size: 200px;
}
</style>
<body>
<div>
<span class="btn btn-success fileinput-button">
<span>上传</span>
<input type="file">
</span>
</div>
</body>
<!-- 最新版本的 Bootstrap 核心 CSS 文件 -->
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" >
<!-- 可选: 包含 jQuery 库 -->
<script src="https://cdn.staticfile.org/jquery/2.1.1/jquery.min.js"></script>
<!-- 可选: 合并了 Bootstrap JavaScript 插件 -->
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.min.js"></script>
</html>
原文地址：https://www.cnblogs.com/kongxianghai/p/5624785.html