Generated by SassMeister.com.

SassMeister-input-HTML.haml

%ul
  %li
    this is my base li


%ul.unique
  %li.unique-li
    this is my unique li

SassMeister-input.scss

// ----
// libsass (v3.0.1)
// ----

li {
  display: block;
  background: green;
}

.unique-li {
  color: blue;
}

SassMeister-output.css

li {
  display: block;
  background: green; }

.unique-li {
  color: blue; }

SassMeister-rendered.html

<ul>
  <li>
    this is my base li
  </li>
</ul>
<ul class='unique'>
  <li class='unique-li'>
    this is my unique li
  </li>
</ul>