Border 
border: width style color;
border: 5px solid red;

To set an element's border.

Borders CSS
Border Style 
border-style: style;

dotted
dashed
solid
double
groove
ridge
inset
outset
none
hidden

Other Properties:
border-width: ;
border-color: ;

Specifies what type of border to display.

Border CSS
Outline 
outline: width style color;
outline: 5px solid red;

To set the outline of an element.

Outline CSS
Border Sides 
border-top-style: ;
border-right-style: ;
border-bottom-style: ; 
border-left-style: ;

border-top-width: ;
border-top-color: ;

To style a specific border side.

Borders CSS
Border Radius 
border-radius: 50%;
        
border-top-left-radius: ;
border-top-right-radius: ;
border-bottom-right-radius: ;
border-bottom-left-radius: ;

To curve borders of an element.

Borders CSS
Outline Offset 
outline-offset: unit;
outline-offset: 5px;

Add space between outline and border.

Outline CSS
Outline Properties 
outline-style:
outline-color:
outline-width:

Outline properties, uses the same values as border.

Outline CSS
Border Image 
border-image: url(image.jpg) 30 stretch;

border-image-source: url('image.jpg');  // to use an image as a border  
border-image-slice: 30;  // divides the image
border-image-repeat: stretch;  // defines how images should fit into their dimensions  
border-image-outset: 15px;  // sets the distance between border and border-box

To use an image for setting borders.

Borders CSS