Why do we put an "a" after .nav but not after .jumbotron?


I passed this already, but I am still wondering, when we stylized the nav bar we said ".nav a{}" etc but then when we stylize jumbotron we don't have the "a" Why?


.nav a is a selector that targets <a> elements in a container with a nav class attribute.

    <ul class="nav">
        <li><a href="#" title="Home page">Home</a></li>
        <li><a href="#" title="Contact page">Contact Us</a></li>
        <li><a href="#" title="About page">About</a></li>