@mixin default_transition($time : 0.2s, $effect : ease-in-out, $delay : 0.2s) {
    -moz-transition: all $time $effect $delay;
    -webkit-transition: all $time $effect $delay;
    -ms-transition: all $time $effect $delay;
    -o-transition: all $time $effect $delay;
    transition: all $time $effect $delay;
}

A { /* pass values to the mixin */
    @include default_transition(1s, ease-in-out, 0.2s)
}

A { /* or leave this empty it will use the default values */
    @include default_transition
}

A:hover {
    color: #006699;
}