Learn Responsive Web Design by Building a Piano - Step 6

Tell us what’s happening:
I have tried to add the code one at a time, all together . Closed out the program and reloaded. Am I missing something?

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" class="black--key"></div>
        <div class="key" class="black--key"></div>
        <div class="key"></div>
        <div class="key" class="black--key"></div>
        <div class="key" class="black--key"></div>
        <div class="key" class="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/106.0.0.0 Safari/537.36

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

Link to the challenge:

This is not how you add multiple class names to an element. If you don’t remember how from the previous projects you worked on then try googling “add multiple classes to element”.

Got it so I don’t have to do multiple class, but combine them all in one. Thanks for nudge in the right direction.