Learn CSS Variables by Building a City Skyline - Step 10

HTML-CSS
1

kindly help me to pass step 10

<!-- file: index.html -->
<!DOCTYPE html>
<html lang="en">    
  <head>
    <meta charset="UTF-8">
    <title>City Skyline</title>
    <link href="styles.css" rel="stylesheet" />
  </head>

  <body>

<!-- User Editable Region -->

    <div class="background-buildings"></div>
    <div class="bb1" href="styles.css"></div> 
    </div>
.bb1{
  width: 10%;
  height: 70%;
}

<!-- User Editable Region -->

  </body>
</html>

/* file: styles.css */
* {
  border: 1px solid black;
  box-sizing: border-box;
}

body {
  height: 100vh;
  margin: 0;
  overflow: hidden;
}

.background-buildings {
  width: 100%;
  height: 100%;
}

Your browser information:

User Agent is: Mozilla/5.0 (X11; CrOS x86_64 13982.82.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.157 Safari/537.36

Challenge: Learn CSS Variables by Building a City Skyline - Step 10

Link to the challenge:

2

This css code goes into styles.css file.
Click on the following button in the challenge:
image

It will be best if you restart the step.