---
id: 5d822fd413a79914d39e98f0
title: Part 40
challengeType: 0
isHidden: true
---
## Description
Gradients in CSS are a way to transition between colors across the distance of an element. They are applied to the `background` property and the syntax looks like this:
```css
gradient-type(
color1,
color2
);
```
In the example, `color1` is solid at the top, `color2` is solid at the bottom, and in between it transitions evenly from one to the next. In `bb1a`, add a gradient of type `linear-gradient` to the `background` property with `--building-color1` as the first color and `--window-color1` as the second.
## Instructions
## Tests
```yml
tests:
- text: test-text
testString: const bb1a = code.match(/\.bb1a\s*{[\s\S]+?[^}]}/g)[0]; assert(/background\s*:\s*linear-gradient\(\s*var\(\s*--building-color1\s*\)\s*,\s*var\(\s*--window-color1\s*\)\s*\)\s*(;|})/g.test(bb1a));
```
## Challenge Seed
```html
freeCodeCamp Skyline Project
```