I'm sorry the title is not particularly explanatory, what I mean is as follows

What I want to achieve with the second CSS selector is "All class b elements that are descendants of class a elements but not descendants of class c elements". As you can see, the selector I've written actually selects all class b elements, regardless of whether or not they are descendants of class c elements. (I.e. I want the central div to appear blue rather than red). Why is my selector not working?

Consider the code in the following:

```css
div {
  background: blue;
  border: 1px solid;
  margin: 20px;
  min-height: 20px;
  max-width: 300px;
}

.a :not(.c) .b {
  background: red;
}
```

```html
<div class="a">
  <div>
    <div class="b">
      <div>
        <div class="c">
          <div>
            <div class="b">
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>
</div>
```