Learn CSS Variables by Building a City Skyline - Step 15

How can i set the background-color using the variable attribute?

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 {
  width: 70%;
  height: 10%;
  var(--building-color1)background-color
}
.bb1b {
  width: 80%;
  height: 10%;
}

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

.bb1d {
  width: 100%;
  height: 70%;
}
    

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 CSS Variables by Building a City Skyline - Step 15

Link to the challenge:

How can i set the background-color using the variable attribute?

Css properties are placed on the left of the colon (look at your width property for an example).

That means you must place the background-color property on a line and on the left of a colon. Then on the right put your variable reference