scss use class in another class code example

Example 1: sass class with another class

.myclass {
  font-weight: bold;
  font-size: 90px;
}

.myotherclass {
  @extend .myclass;
  color: #000000;
}

Example 2: scss extend

.error:hover {
  background-color: #fee;
}

.error--serious {
  @extend .error;
  border-width: 3px;
}