Bootstrap4 按钮
Bootstrap4上提供了不同样式的按钮，这些按钮支持一系列上下文变量、尺寸、状态等设置。
按钮样式：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap4 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<div class="container">
<h2>按钮样式</h2>
<button type="button" class="btn">基本按钮</button>
<button type="button" class="btn btn-primary">主要按钮</button>
<button type="button" class="btn btn-secondary">次要按钮</button>
<button type="button" class="btn btn-success">成功</button>
<button type="button" class="btn btn-info">信息</button>
<button type="button" class="btn btn-warning">警告</button>
<button type="button" class="btn btn-danger">危险</button>
<button type="button" class="btn btn-dark">黑色</button>
<button type="button" class="btn btn-light">浅色</button>
<button type="button" class="btn btn-link">链接</button>
</div>
</body>
</html>
按钮类可用于 <a>, <button>, 或 <input> 元素上:
实例：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap4 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<h2>按钮元素</h2>
<a href="#" class="btn btn-info" role="button">链接按钮</a>
<button type="button" class="btn btn-info">按钮</button>
<input type="button" class="btn btn-info" value="输入框按钮">
<input type="submit" class="btn btn-info" value="提交按钮">
</div>
</body>
</html>按钮设置边框：
需要一个按钮，但是不要他们自带的背景颜色？我们可以使用.btn-outline类来实现。
实例：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap4 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<h2>按钮设置边框</h2>
<button type="button" class="btn btn-outline-primary">主要按钮</button>
<button type="button" class="btn btn-outline-secondary">次要按钮</button>
<button type="button" class="btn btn-outline-success">成功</button>
<button type="button" class="btn btn-outline-info">信息</button>
<button type="button" class="btn btn-outline-warning">警告</button>
<button type="button" class="btn btn-outline-danger">危险</button>
<button type="button" class="btn btn-outline-dark">黑色</button>
<button type="button" class="btn btn-outline-light text-dark">浅色</button>
</div>
</body>
</html>按钮大小
Bootstrap 4 可以设置按钮的大小，.btn-lg类可以设置大号按钮，.btn-sm类可以设置小号按钮。
实例：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap4 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<h2>按钮大小</h2>
<button type="button" class="btn btn-primary btn-lg">大号按钮</button>
<button type="button" class="btn btn-primary">默认按钮</button>
<button type="button" class="btn btn-primary btn-sm">小号按钮</button>
</div>
</body>
</html>块级按钮
通过添加 .btn-block 类可以设置块级按钮：
实例：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap4 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<h2>块级按钮</h2>
<button type="button" class="btn btn-primary btn-block">按钮 1</button>
<button type="button" class="btn btn-default btn-block">按钮 2</button>
<h2>大的块级按钮</h2>
<button type="button" class="btn btn-primary btn-lg btn-block">按钮 1</button>
<button type="button" class="btn btn-default btn-lg btn-block">按钮 2</button>
<h2>小的块级按钮</h2>
<button type="button" class="btn btn-primary btn-sm btn-block">按钮 1</button>
<button type="button" class="btn btn-default btn-sm btn-block">按钮 2</button>
</div>
</body>
</html>激活和禁用的按钮
按钮可设置为激活或者禁止点击的状态。
.active 类可以设置按钮是可用的， disabled 属性可以设置按钮是不可点击的。 注意 <a> 元素不支持 disabled 属性，你可以通过添加 .disabled 类来禁止链接的点击。
实例：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap4 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<h2>按钮状态</h2>
<button type="button" class="btn btn-primary">主要按钮</button>
<button type="button" class="btn btn-primary active">点击后的按钮</button>
<button type="button" class="btn btn-primary" disabled>禁止点击的按钮</button>
<a href="#" class="btn btn-primary disabled">禁止点击的链接</a>
</div>
</body>
</html>