Example using placeholder selector

SassMeister-input.sass

// ----
// Sass (v3.4.21)
// Compass (v1.0.3)
// ----

%loader-base-config
  color: red
  position: fixed
  box-sizing: border-box
  left: -9999px
  top: -9999px
  width: 0
  height: 0
  overflow: hidden
  z-index: 999999

  &:after,
  &:before
    box-sizing: border-box
    display: none

  &.is-active
    background-color: blue
    width: 100%
    height: 100%
    left: 0
    top: 0

    &:after,
    &:before
      display: block
      
.class-1 
  @extend %loader-base-config
  
  border: 1px solid red
  
.class-2
  @extend %loader-base-config
  
  text-decoration: underline
  

SassMeister-output.css

.class-1, .class-2 {
  color: red;
  position: fixed;
  box-sizing: border-box;
  left: -9999px;
  top: -9999px;
  width: 0;
  height: 0;
  overflow: hidden;
  z-index: 999999;
}
.class-1:after, .class-2:after, .class-1:before, .class-2:before {
  box-sizing: border-box;
  display: none;
}
.is-active.class-1, .is-active.class-2 {
  background-color: blue;
  width: 100%;
  height: 100%;
  left: 0;
  top: 0;
}
.is-active.class-1:after, .is-active.class-2:after, .is-active.class-1:before, .is-active.class-2:before {
  display: block;
}

.class-1 {
  border: 1px solid red;
}

.class-2 {
  text-decoration: underline;
}