Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.1)
// Compass (v0.13.alpha.10)
// ----

@import "compass";

// class selectors to be @extended
// these could also use % to be silent/placeholder selectors
.size-3xl {
    @include rem(font-size, 60px);
}
.size-2xl {
    @include rem(font-size, 40px);
}

// mapping the class selector properties onto some structural classes
.heading1 {
    @extend .size-3xl;
}
.heading1-small {
    @extend .heading1;
    @extend .size-2xl;
}

SassMeister-output.css

.size-3xl, .heading1, .heading1-small {
  font-size: 60px;
  font-size: 3.75rem;
}

.size-2xl, .heading1-small {
  font-size: 40px;
  font-size: 2.5rem;
}