33) Nesting.css

CSS nesting is the practice of placing selectors inside one another, providing a structured way to target and style specific HTML elements. 
It reduces repetition, resulting in cleaner and more concise code.

CSS:
.parent {
  color: black;
  background-color: red;

  & span {
    color: blue;
  }
}

This is equivalent to:

.parent {
  color: black;
  background-color: red;
}

.parent span {
  color: blue;
}

The '&' is needed at the beginning of each selector for the nesting to be valid. 
We can think of using '&' as referencing the parent selector.

Example:
HTML:
<header>
  <div class="logo">
    BB Academy
  </div>
  <nav class="menu">
    <ul class="menu-list">
      <li class="menu-item">
        <a href="#">Home</a>
      </li>
      <li class="menu-item">
        <a href="#">About</a>
      </li>
      <li class="menu-item">
        <a href="#">Services</a>
      </li>
      <li class="menu-item">
        <a href="#">Contact</a>
      </li>
    </ul>
  </nav>
</header>

CSS:
header {
  display: flex;
  justify-content: space-between;
  padding: 10px;
  background-color: lightcyan;
}

.logo {
  font-size: 2rem;
  color: red;
  &:hover {
    color: blue;
  }
}

.menu {
  padding: 10px;
  & .menu-list {
    list-style: none;
    margin: 0;
    padding: 0;
    
    & .menu-item {
      display: inline-block;
      margin-right: 20px;
      
      & a {
        text-decoration: none;
        border: 1px solid black;
        border-radius: 5px;
        color: red;
        padding: 10px;
        
        &:hover {
          background-color: blue;
          color: white;
        }
      }
    }
  }