The border property can be used to visually define a page element's outer edge.

In CSS, the border property's value requires three parts:

1. thickness: Sets the thickness of the border, using pixels, ems, or rems.

2. type: Sets the border type. Common options are solid, dotted, and dashed. There are many others.

3. color: sets the border's color, using named colors, HEX, or RGB values.

The CSS below gives a paragraph element a solid black border that is 2 pixels thick:

p {
  border: 2px solid black; 
}