Виталий Инчин ☢

@mixin example{
   border: 1px solid red;
}

.class1{
   @include example;
}

.class2{
   @include example;
}

.class1{
   border: 1px solid red;
}

.class2{
   border: 1px solid red;
}

%_example{
   border: 1px solid red;
}

.class1{
   @extend %_example;
}

.class2{
   @extend %_example;
}

.class1,  .class2{
   border: 1px solid red;
}

@mixin example($width, $color){
   border: $width solid $color;
}

.class1{
   @include example(1px, red);
}

.class2{
   @include example(2px, yellow);
}

.class1{
   border: 1px solid red;
}

.class2{
   border: 2px solid yellow;
}