By default, an element has no border. You can add a border to an element by using <b>border</b> keyword. By using this keyword, you can add 3 values: the width in px, border type eg. solid, dashed, dot, etc., and the color of the border.
.border { border: 3px solid blue; }
<div class="border"> </div>
You can also set the border by values eg. border-right, border-top, border-left, border-bottom, border-style and border-color.
.border { border-right: 1px; border-top: 2px; border-left: 3px; border-bottom: 4px; border-color: blue; border-style: solid }
You can have a rounded borders using border-radius keyword.
.border { border: 3px solid blue; border-radius: 5px; }