This is probably one of the most-used CSS3 properties and it's so easy to implement. Learning the border-radius property is a breeze. Let's get started with some example code.
Simple Rounded Corners
The code:
.box {
background: #f9f9e0;
padding: 10px;
border: 1px solid #cfcf99;
-moz-border-radius: 10px;
-webkit-border-radius: 10px;
border-radius: 10px;
}
background: #f9f9e0;
padding: 10px;
border: 1px solid #cfcf99;
-moz-border-radius: 10px;
-webkit-border-radius: 10px;
border-radius: 10px;
}
The -moz- prefix is for Firefox. The -webkit- prefix is for Safari and Chrome.
The outcome:
This box should have rounded corners for Firefox.
How The border-radius Property Works
First, let's go over the syntax. I used the shorthand property so all corners have the same value. The original properties are:
border-bottom-left-radius
border-bottom-right-radius
border-top-left-radius
border-top-right-radius
border-bottom-right-radius
border-top-left-radius
border-top-right-radius
The border-radius properties can each accept either one or two values, expressed as a length (px) or a percentage (%) - percentages refer to the corresponding dimensions of the border box.
The border-radius Syntax:
border-radius: [ px | % ] [ px | % ]
The code:
.box {
-moz-border-radius: 10% 10px 10% 10px;
-webkit-border-radius: 10% 10px 10% 10px;
border-radius: 10% 10px 10% 10px;
}
-moz-border-radius: 10% 10px 10% 10px;
-webkit-border-radius: 10% 10px 10% 10px;
border-radius: 10% 10px 10% 10px;
}
The outcome:
This box should have rounded corners for Firefox.
The Mozilla implementation also behaves slightly differently from the specification when percentages are supplied. You can read more on the Mozilla Developer Center.
If all four values are supplied, these represent the top-left, top-right, bottom-right and bottom-left radii respectively. If bottom-left is omitted it is the same as top-right, if bottom-right is omitted it is the same as top-left, and if only one value is supplied it is used to set all four radii equally.
For more information on the border-radius property visit W3C on CSS Backgrounds and Borders.