15.use-an-id-attribute-to-style-an-element.html

<link
  href="https://fonts.googleapis.com/css?family=Lobster"
  rel="stylesheet"
  type="text/css"
/>
<style>
  .red-text {
    color: red;
  }

  h2 {
    font-family: Lobster, monospace;
  }

  p {
    font-size: 16px;
    font-family: monospace;
  }

  .thick-green-border {
    border-color: green;
    border-width: 10px;
    border-style: solid;
    border-radius: 50%;
  }

  .smaller-image {
    width: 100px;
  }

  .silver-background {
    background-color: silver;
  }

  #cat-photo-form {
    background-color: green;
  }
</style>

<h2 class="red-text">CatPhotoApp</h2>
<main>
  <p class="red-text">Click here to view more <a href="#">cat photos</a>.</p>

  <a href="#"
    ><img
      class="smaller-image thick-green-border"
      src="https://bit.ly/fcc-relaxing-cat"
      alt="A cute orange cat lying on its back."
  /></a>

  <div class="silver-background">
    <p>Things cats love:</p>
    <ul>
      <li>cat nip</li>
      <li>laser pointers</li>
      <li>lasagna</li>
    </ul>
    <p>Top 3 things cats hate:</p>
    <ol>
      <li>flea treatment</li>
      <li>thunder</li>
      <li>other cats</li>
    </ol>
  </div>

  <form
    action="https://freecatphotoapp.com/submit-cat-photo"
    id="cat-photo-form"
  >
    <label><input type="radio" name="indoor-outdoor" checked /> Indoor</label>
    <label><input type="radio" name="indoor-outdoor" /> Outdoor</label><br />
    <label><input type="checkbox" name="personality" checked /> Loving</label>
    <label><input type="checkbox" name="personality" /> Lazy</label>
    <label><input type="checkbox" name="personality" /> Energetic</label><br />
    <input type="text" placeholder="cat photo URL" required />
    <button type="submit">Submit</button>
  </form>
</main>