fade out doesn’t work

Guys, why does fade in work, but fade out doesn't. I want it to stay for a while when a user moves a cursor away…
This is code:

Code (text):

        .tooltip {

            border-bottom: 1px dotted #000000; color: #000000; outline: none;

            cursor: help; text-decoration: none;

            position: relative;

        }

        .tooltip span {

            margin-left: -999em;

            position: absolute;

            visibility:hidden;

            opacity:0;…

fade out doesn't work

See original post by budimir