Learn CSS Variables by Building a City Skyline - Step 23

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

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

  <div class="background-buildings">
    <div class="bb1">
      <div class="bb1a"></div>
      <div class="bb1b"></div>
      <div class="bb1c"></div>
      <div class="bb1d"></div>
    <div class="bb2"></div>
    <div class="bb3"></div>
    <div class="bb4"></div>
/* file: styles.css */
* {
border: 1px solid black;
box-sizing: border-box;

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

.background-buildings {
width: 100%;
height: 100%;
display: flex;
align-items: flex-end;
justify-content: space-evenly;

.bb1 {
width: 10%;
height: 70%;
display: flex;
flex-direction: column;
align-items: center;
--building-color1: #aa80ff;
--building-color2: #66cc99;

.bb1a {
width: 70%;
height: 10%;
background-color: var(--building-color1);

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

.bb1c {
width: 90%;
height: 10%;
background-color: var(--building-color1);

.bb1d {
width: 100%;
height: 70%;
background-color: var(--building-color1);
.bb2 {
width: 10%;
height: 50%;
background-color: var(--building-color2, fallback-green);
.bb3 {
width: 10%;
height: 55%;

.bb4 {
width: 11%;
height: 58%;
  **Your browser information:**

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

Challenge: Learn CSS Variables by Building a City Skyline - Step 23

Link to the challenge:

the color name is just green, it will be fallback if building-color2 is not working for some reason


Did you find the answer?
I’ve the same problem…

Hi @simaao.web

Please create a new thread using the “Ask for Help” Button when you are stuck.


it didn’t work for me when i wrote it as as fallback-green, i deleted fallback- and just wrote green and it worked for me, hope that makes sense

background-color: var(–building-color2, fallback-green); this didn’t work
Mod edit: solution removed
this worked for me


Hi there Edgar,

I appreciate seeing you contributing to the forum by helping others but please do try to do this in future without posting code solutions. Hints and tips are very welcome though.

Thanks for your understanding!

Thank you soooo much

It is great that you solved the challenge, but instead of posting your full working solution, it is best to stay focused on answering the original poster’s question(s) and help guide them with hints and suggestions to solve their own issues with the challenge.

We are trying to cut back on the number of spoiler solutions found on the forum and instead focus on helping other campers with their questions and definitely not posting full working solutions.

I was just struggling with the same topic. But I got it. The answer lies in careful and exact reading what we have to code. The fallback value should be “green”. So the code is only the word green without the word fallback. OK?!

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