Properties

outline

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/* width | style | color */
outline: 1px solid white;

/* Global values */
outline: inherit;
outline: initial;
outline: unset;

The outline property in CSS draws a line around the outside of an element. It’s similar to border except that:

• You can’t specify particular sides
• It’s not a part of the box model, so it won’t effect the position of the element or adjacent elements
• It doesn’t respect border-radius (makes sense - it’s not a border)
• It isn’t always rectangular. If the outline goes around an inline element with different font-sizes, for instance, Opera will draw a staggered box around it all.

Often used for accessibility reasons, to emphasize a link when tabbed to without affecting positioning and in a different way than hover.

Selectors

Pseudo class selectors are CSS selectors with a colon preceding them.

a:hover {

}

Tools

• Autoprefixer CSS Online
• Prefix free: Break free from CSS vendor prefix hell!
• Visual Dictionary of CSS