you don't necessarily have to duplicate code blocks all the time since you can declare a definition for multiple styles:

  .uno {
    color: green;
    font-size: 18px;
    text-align: center;
  }
  .dos {
    color: green;
    font-size: 18px;
  }

can become

  .uno, .dos {
    color: green;
    font-size: 18px;
  }
  .uno {
    text-align: center;
  }

also, as others have pointed out, nesting is kind of there in the form of a hierarchy. child elements will get parent styles for most properties.