h3 {
  font-size: 20px
  margin-bottom: 10px

  .some-parent-selector & {
        font-size: 24px
        margin-bottom: 20px
  }
}

h3 {
  font-size: 20px;
  margin-bottom: 10px;
}
.some-parent-selector h3 {
  font-size: 24px;
  margin-bottom: 20px;
}

.some-parent-selector {
    font-size: 24px
    margin-bottom: 20px

    a& {
        ...
    }
}

.some-parent-selector {
    font-size: 24px
    margin-bottom: 20px
}
a.some-parent-selector {
    ...
}

.some-parent-selector {
        font-size: 24px;
        margin-bottom: 20px;

       a#{&}{
            margin-bottom: 20px
        }
    }

.some-parent-selector {
  font-size: 24px;
  margin-bottom: 20px;
}
.some-parent-selector a.some-parent-selector {
  margin-bottom: 20px;
}

.some-parent-selector {
    font-size: 24px;
    margin-bottom: 20px;

   @at-root a#{&}{
        margin-bottom: 20px
    }
}

.some-parent-selector {
  font-size: 24px;
  margin-bottom: 20px;
}
a.some-parent-selector {
  margin-bottom: 20px;
}