test-less.css

.message,
.success,
.error,
.warning {
  border: 1px solid #ccc;
  padding: 10px;
  color: #333;
}
.success {
  border-color: green;
}
.error {
  border-color: red;
}
.warning {
  border-color: yellow;
}

test-sass.css

.message, .success, .error, .warning {
  border: 1px solid #cccccc;
  padding: 10px;
  color: #333;
}

.success {
  border-color: green;
}

.error {
  border-color: red;
}

.warning {
  border-color: yellow;
}

test.less

.message {
  border: 1px solid #ccc;
  padding: 10px;
  color: #333;
}

.success {
  .message();
  border-color: green;
}

.error {
  .message();
  border-color: red;
}

.warning {
  .message();
  border-color: yellow;
}

test.scss

.message {
  border: 1px solid #ccc;
  padding: 10px;
  color: #333;
}

.success {
  @extend .message;
  border-color: green;
}

.error {
  @extend .message;
  border-color: red;
}

.warning {
  @extend .message;
  border-color: yellow;
}