Nested properties should define at least two properties. If they do not, either it means that some expected properties are missing or that they can be converted into simple property declarations.

Noncompliant Code Example

.mybox {
  padding: {     /* Noncompliant: Forgot to add bottom declaration? */
    left: 20px;
  }
}

Compliant Solution

.mybox {
  padding: {
    left: 20px;
    bottom: 10px;
  }
}

OR

.mybox {
  padding-left: 20px;
}