Parameter| Details | —— | —— | dotted | dotted outline | dashed| dashed outline| solid | solid outline | double| double outline | groove| 3D grooved outline, depends on the outline-color value | ridge| 3D ridged outline, depends on the outline-color value|
|inset|3D inset outline, depends on the outline-color value| |outset|3D outset outline, depends on the outline-color value| |none|no outline| |hidden|hidden outline|
outline
is now described in Basic UI, a CSS Module Level 3 (it was already described in REC CSS2.1)
Outline property is defined by default in browsers for focusable elements in :focus
state.
It shouldn’t be removed, see http://outlinenone.com which states:
What does the outline property do?
It provides visual feedback for links that have “focus” when navigating a web document using the TAB key (or equivalent). This is especially useful for folks who can’t use a mouse or have a visual impairment. If you remove the outline you are making your site inaccessible for these people. (…)
Interesting related examples on Stack Overflow: