CSS Selector help

What is a CSS Selector? Please read https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Selectors

In the CSS Selector Filter field, you enter the selector not the HTML

So for example if the HTML is

<div class="points">
  <span id="interesting">
  57 points
  </span>
</div>

the selector would be .points #interesting