Selector Lists sass

Nested rules are clever about handling selector lists (that is, comma-separated selectors). Each complex selector (the ones between the commas) is nested separately, and then they’re combined back into a selector list.

code sass

.alert, .warning {
  ul, p {
    margin-right: 0;
    margin-left: 0;
    padding-bottom: 0;
  }
}

code css

.alert ul, .alert p, .warning ul, .warning p {
  margin-right: 0;
  margin-left: 0;
  padding-bottom: 0;
}