What the use of Mixins in SASS

CSS does not support mixins Any repeated code must be repeated in each location. A mixin is a section of code that contains any valid Sass code. Whenever a mixin is called, the result of translating the mixin is inserted at the calling location. Mixins allow for efficient and clean code repetitions, as well as easy alteration of code.

@mixin table-base {
  th {
    text-align: center;
    font-weight: bold;
  }
  td, th {padding: 2px}
}
 
#data {
  @include table-base;
}

Would compile to:

#data th {
  text-align: center;
  font-weight: bold;
}
#data td, #data th {
  padding: 2px;
}