border-radius

The border-radius CSS property allows Web authors to define how rounded border corners are. The curve of each corner is defined using one or two radii, defining its shape: circle or ellipse.
 
The radius applies to the whole background, even if the element has no border; the exact position of the clipping is defined by the background-clip property.
 
This property is a shorthand to set the four properties border-top-left-radius, border-top-right-radius, border-bottom-right-radius and border-bottom-left-radius.

Example

<!DOCTYPE HTML>
<html>
    <head>
        <title>CSS Tutorials</title>
        <style> 
            div {
				border-radius:20px;
                width:200px;
				height:200px;
				background-color:#D9FBC4;
            }
        </style>
    </head>
    <body>
        <div>
            border-left-style
        </div>
    </body>
</html>