Border

Shorthand to set the 3 properties:

element { border: border-width border-style border-color ;}

This shorthand is equivalent to the following:

element {
  border-width: length | thin | medium | thick | inherit ;
  border-style: style ;
  border-color:  color ;
}

Alternatively you can choose to inherit from a parent element: border: inherit ;

These three properties are themselves shorthand properties, for example border-style can set different styles for top, bottom, left and right borders. If you use the border shorthand it will set all 4 to the same value.

The Border-Style property must be set for the Border-Width or Border-Color properties to have any effect.

The default property values, any value that is not specified in the shorthand will be set to the default:

  border-width: medium;
  border-style: none;
  border-color: 0;

Examples

Set the border of H1 to a 2px solid green line:

h1 {border: 2px solid green ;}

Try it:

Browser Support: All major browsers (CSS 1) Web browsers will interpret the shortcut values in any order.

“I am the kind of person who doesn't recognize borders. I don't understand why we think it is okay to keep someone within one border when they are unable to feed their family when they could be getting help somewhere else. I don't see people as different so I don't understand the idea of borders in this world” ~ Angelina Jolie

Related:

border - MDN Web Docs.
border-bottom - Shorthand to set all the border-bottom properties.
border-left - Shorthand to set all the border-left properties.
border-right - Shorthand to set all the border-right properties.
border-top - Shorthand to set all the border-top properties.
The CSS Box Model