使用Bootstrap创建一个蓝色按钮（主要）
使用Bootstrap中的.btn-primary类在Bootstrap中创建蓝色的主按钮-
示例
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap Example</title>
<link rel = "stylesheet" href = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css">
<script src = "https://cdn.staticfile.org/jquery/3.3.1/jquery.min.js"></script>
<script src = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
</head>
<body>
<p>Click below if you want to know the result:</p>
<button type = "button" class = "btn btn-primary">Result</button>
</body>
</html>