Here is a brief definition and the explanation on the usage of the Css3 Borders-Border radius property
CSS3 Border-radius The CSS3 border-radius Property helps you provide "rounded corners" for an element.
border-radius The border-radius property is a shorthand property for the border-top-left-radius, border-top-right-radius, border-bottom-right-radius and border-bottom-left-radius properties.
If you specify only one value for the border-radius property, this radius will be applied to all 4 corners. Four values: First value applies to top-left, second value applies to top-right, third value applies to bottom-right, and fourth value applies to bottom-left corner. Three values: First value applies to top-left, second value applies to top-right and bottom-left, and third value applies to bottom-right.Two values: First value applies to top-left and bottom-right corner, and the second value applies to top-right and bottom-left corner.One value: All four corners are rounded equally.