CSS

CSS stands for Cascading Style Sheets. It's one of the three primary technologies of the web that runs in the browser (including HTML and JavaScript). CSS is the technology that creates the stylistic "look" for a website, normally by writing rulesets that "select" areas of the DOM to apply properties to. For example, given this HTML, we can stylize the user-item DOM elements with the CSS that follows in the next example:

<div class="results">

  <div class="user-item">
    <h2>Dhruv Patel</h2>
    <a href="/profile/1">View Profile</a>
  </div>

  <div class="user-item">
    <h2>Joe Fleming</h2>
    <a href="/profile/2">View Profile</a>
  </div>

</div>

This CSS "selects" all of the DOM elements with a .user-item class above to give them a background color:

.user-item {
  background-color: #00a9ff;
}