Learn CSS Variables by Building a City Skyline - Step 15

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>City Skyline</title>
  <link href="styles.css" rel="stylesheet" />   
</head>

<body>
  <div class="background-buildings">
    <div class="bb1">
      <div class="bb1a"></div>
      <div class="bb1b"></div>
      <div class="bb1c"></div>
      <div class="bb1d"></div>
    </div>
  </div>
</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%;
}

.bb1 {
width: 10%;
height: 70%;
display: flex;
flex-direction: column;
align-items: center;
--building-color1: #999;
}

.bb1a {
var(--building-color1): #999;
width: 70%;
height: 10%;
}
.bb1b {
width: 80%;
height: 10%;
}

.bb1c {
width: 90%;
height: 10%;
}

.bb1d {
width: 100%;
height: 70%;
}
  
  **Your browser information:**

User Agent is: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36

Challenge: Learn CSS Variables by Building a City Skyline - Step 15

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