Avoid Divitis, Classitis, Tagitis, etc.

<div class="header">Our Solar System</div>

or even

<div class="header"><h1>Our Solar System</h1></div>

<h1>Our Solar System</h1>

<div class="basketball">
  <ul>
    <li>Mark Few</li>
    <li>Roy Williams</li>
    <li>Thad Matta</li>
    ...
  

<ul class="basketball">
    <li>Mark Few</li>
    <li>Roy Williams</li>
    <li>Thad Matta</li>
    ...