要将左圆角设置为元素，请使用Bootstrap 4中的rounded-left类。
在任何元素上使用类，例如<div>-
<div class="one rounded-left"> </div>
我们还包括了一个用于设置<div>样式的类-
.one {
width: 200px;
height: 100px;
background-color: maroon;
margin: 8px;
}让我们看一个实现左舍入类的例子-
<!DOCTYPE html>
<html lang="en">
<head>
<title>Bootstrap Example</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/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/4.1.0/js/bootstrap.min.js"></script>
<style>
.one {
width: 200px;
height: 100px;
background-color: maroon;
margin: 8px;
}
</style>
</head>
<body>
<div class="container">
<h2>Rounded Corner</h2>
<p>We have two rectangles with left rounded corner:</p>
<div class="one rounded-left"></div>
<div class="one rounded-left"></div>
</div>
</body>
</html>