Firefox Browser on CSS exercises

This is a firefox browser issue, but I just thought i’d point this out if anyone encounters the same issue. What I noticed was some browser extensions/plugins can affect the completion of an exercise.

The following is from “Basic CSS: Use CSS Selectors to Style Elements”.

  h2 { 
    color: blue;

  <p>Click here to view more <a href="#">cat photos</a>.</p>

  <a href="#"><img src="" alt="A cute orange cat lying on its back."></a>

    <p>Things cats love:</p>
      <li>cat nip</li>
      <li>laser pointers</li>
    <p>Top 3 things cats hate:</p>
      <li>flea treatment</li>
      <li>other cats</li>

  <form action="">
    <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>

The very code above works and solves the exercise, however it is not recognised as accepted when I used Firefox with a dark mode extension I had installed, but after disabling it, it worked. I observed this will be the case for exercises that require you to change colors.


This is a known issue for any browser. Extensions that change the colors in your browser work by changing your CSS. This necessarily interferes with tests that check your CSS.


Thanks for informing, this was totally new to me.

Oooooo good to know, that makes a lot of sense. Is there any extension or add-on out there that can create that effect in any other way than using CSS (just out of curiosity)?

you can switch the native dark mode in the settings of your account, that one will
not interfere with the tests


Thanks for informing, this was totally new to me.