The latest news carousel's "previous" button is pointing forward

## 🐛 Bug Report

### Current behavior

_A clear and concise description of the bug you found in amp.dev._

Please also provide:
- Page link: https://amp.dev/
- (Optional) Screenshots/videos:


### Expected behavior/code

_A clear and concise description of what you expected to happen._

On the home page, the latest news carousel's "previous" button is pointing forward (to the right) instead of backward (to the left) as can be seen both in the screenshot provided.

### Reproduction procedure
Please provide the steps to reproduce the problem:

1. Visit [https://amp.dev](https://amp.dev)
2. View the "Latest news" section's carousel buttons
3. Click the "next" button
4. Notice that "previous" is still pointing in the wrong direction

- What browser are you using? Mozilla Firefox Developer Edition
- What O/S are you using? Windows Server 2019

- [x] I would like to work on this issue and submit a pull request.

/cc @CrystalOnScript