In box model, border comes between margin and padding. Margin and padding are use to get some invisible space among other HTML elements. Border is outer visible area of HTML element.
You can set border color, style and size individual or combine.
/* syntex */Shortest way to write border property
border: <width> <style> <color>;
border:2px solid red;
above properties can write in another way
border-size: 2px;
border-type: solid;
border-color: red;
each border with different style also possible, in clock wise direction top, right, bottom, left
border-size: 2px 3px 1px 5px;
border-type: dotted dash solid double;
border-color: red green blue yellow;