* Spoiler *

The use of `:not` is way more powerful that I usually remember. For example, the second exercise asks to select all the <p> except the one with class="foo"

  <div>
    <p></p>
    <p class="foo"></p>
    <p></p>
    <p></p>
  </div>

This can be done with

  p:not(.foo)

But also by selecting every thing that we don't want and then negating that.

  :not(div, .foo)