Details

Reports when you define the same selector twice in a single sheet.

Bad

h1 {
  margin: 10px;
}

.baz {
  color: red;
}

// Second copy of h1 rule
h1 {
  text-transform: uppercase;
}

Good

h1 {
  margin: 10px;
  text-transform: uppercase;
}

.baz {
  color: red;
}

Combining duplicate selectors can result in an easier to read sheet, but occasionally the rules may be purposely duplicated to set precedence after a rule with the same CSS specificity. However, coding your stylesheets in this way makes them more difficult to comprehend, and can usually be avoided.

You can specify that rule sets which can be nested within another rule set must be nested via the force_nesting option, e.g.

Bad

h1 {
  color: #fff;
}

h1.new {
  color: #000;
}

Good

h1 {
  color: #fff;

  &.new {
    color: #000;
  }
}