Links get a dashed box when you click on them. This is ugly specially if your link it's an image.
This dash actually show witch link is on focus. Useful if you navigate with tab...
This CSS remove outline but keep accessibility by hidden it only when the user click on the link (the new page is loading).
a:focus {
outline: 1px dotted;
}
a:active {
outline: 0;
}
Enjoy!