A detailed introduction to Outline:none in CSS

When the element gets focus, the focus frame is 0.
For example, the current page, you use the TAB key to switch, text links, search boxes, buttons, and so on the outside there will be a dashed box (or highlight box), the current element has been the focus, you can manipulate it.
This feature is typically prepared for users who use keyboard operations.
Some links-such as a picture link, you don't want him to break the design of the dashed box, you can use this method.

Recommendations are generally not removed, only in some areas that affect the beauty of the design. After all, this focus frame is very helpful for keyboard users.

Definition and usage
The Outline-style property is used to set the style of the entire outline of an element. The style cannot be none, otherwise the outline does not appear.

A outline (contour) is a line that is drawn around an element, at the periphery of the edge of the bounding rectangle, that acts as an element of prominence. The Outline property sets the contour line around the element.

NOTE: Always declare the Outline-style property before the Outline-color property. An element can change the color of its outline only after it has obtained an outline.

Note: Footprints do not occupy space or are not necessarily rectangles.

Default value: None

To set the style of the outline:

P  {  outline-style:dotted;  }

Browser support
All major browsers support the Outline-style property.

Only in the rules! Internet Explorer supports the Outline-style property when DOCTYPE.
Possible values
Value Description
None defaults. Defines no outlines.
Dotted defines a point-shaped outline.
Dashed defines the dashed outline.
Solid defines the solid outline.
Double defines a two-line outline. The width of the double line is equal to the value of Outline-width.
Groove defines a 3D groove profile. This effect depends on the Outline-color value.
Ridge defines a 3D convex groove profile. This effect depends on the Outline-color value.
Inset defines a 3D concave edge profile. This effect depends on the Outline-color value.
Outset defines a 3D convex edge profile. This effect depends on the Outline-color value.
inherit specifies that the outline style settings should be inherited from the parent element.