@mixin transition($val...) { -webkit-transition: $val; -moz-transition: $val; transition: $val; } btn-a { @include transition(color 0.3s ease-in, background 0.5s ease-out); }
Without adding the … to $val the argument would think that there are 2 arguments being passed in. By adding … the $val… becomes a variable argument and can handle the passed value.