// mixin for clearfix
@mixin clearfix() {
  &:before,
  &:after {
    content: " ";
    display: table;
  }

  &:after {
    clear: both;
  }
}

.class {
  padding: 10px;
  @include clearfix();
}

.base {
  color: red;
}

// placeholder
%base {
  padding: 12px;
}

.foo {
  @extend .base;
}

.bar {
  @extend %base;
}