Learn Responsive Web Design by Building a Piano - Step 6

Tell us what’s happening:
Describe your issue in detail here.

Your code so far

<!-- file: index.html -->
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Piano</title>
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  </head>
  <body>
    <div id="piano">
      <div class="keys">
        <div class="key"></div>
        <div class="key, black--key"></div>
        <div class="key, black--key"></div>
        <div class="key"></div>
        <div class="key, black--key"></div>
        <div class="key, black--key"></div>
        <div class="key, black--key"></div>
      </div>
    </div>
  </body>
</html>
/* file: styles.css */

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/105.0.0.0 Safari/537.36

Challenge: Learn Responsive Web Design by Building a Piano - Step 6

Link to the challenge:

There should be no comma in the class name. If you want to give multiple class names you only need space to separate them and not commas.
So your code should be like:

mod edit: solution redacted