test.html

<div class="wall-full-screen-template other-class">
  <ul class="foo">
    <li class="bar">a</li>
    <li class="bar">b</li>
    <li class="bar">c</li>
    <li class="bar">d</li>
    <li class="bar baz">e</li>
  </ul>
</div>

test.less

.wall-full-screen-template {
  .foo {
      // this is applied to any .foo inside of a .wall-full-screen-template (children, grandchildren, etc)

    .bar {
      // this is applied to any .bar inside a .foo inside a .wall-full-screen-template

      &.baz {
        // this is applied to any .bar.baz inside a .foo inside a .wall-full-screen-template
      }
    }
  }


  &.other-class {
    //this gets applied to any element w/ both .wall-full-screen-template and other-class
  }
}