---
id: 612e89562043183c86df287c
title: Step 9
challengeType: 0
dashedName: step-9
---
# --description--
Browsers can apply default margin and padding values to specific elements. To make sure your piano looks correct, you need to reset the box model.
Add an `html` rule selector to your CSS file, and set the `box-sizing` property to `border-box`.
# --hints--
You should have an `html` selector.
```js
assert(new __helpers.CSSHelp(document).getStyle('html'));
```
Your `html` selector should have the `box-sizing` property set to `border-box`.
```js
assert(new __helpers.CSSHelp(document).getStyle('html')?.boxSizing === 'border-box');
```
# --seed--
## --seed-contents--
```html
Piano