Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.14)
// Compass (v1.0.3)
// ----

/* box */
.my-box {
  padding: 10px;
  border-width: 3px;
  border-style: solid;
  &.is-error {
    border-color: red;
  }
  &.is-current {
    border-color: green;
  }
}
/* input */
.my-input {
  $box: ".my-box";
  //.parent.errorの時の、.inputの状態
  #{$box}.is-error &{
    background-color: red;
  }
  #{$box}.is-current &{
    background-color: green;
  }
}

SassMeister-output.css

/* box */
.my-box {
  padding: 10px;
  border-width: 3px;
  border-style: solid;
}
.my-box.is-error {
  border-color: red;
}
.my-box.is-current {
  border-color: green;
}

/* input */
.my-box.is-error .my-input {
  background-color: red;
}
.my-box.is-current .my-input {
  background-color: green;
}