docs: modify the sample style error

[DimplesY]

Description

修改了文档当中的画布示例设置的样式

[x6-bot]

👋 @DimplesY

💖 Thanks for opening this pull request! 💖

Please follow the contributing guidelines. And we use semantic commit messages to streamline the release process.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add graph.scale() method
• docs: graph.getShortestPath is now available

Things that will help get your PR across the finish line:

• Follow the TypeScript, JavaScript, CSS and React coding style.
• Run npm run lint locally to catch formatting errors earlier.
• Document any user-facing changes you've made.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[x6-bot]

👋 @DimplesY

Congrats on merging your first pull request! 🎉🎉🎉