[Bug report] wrong code block scroll bar style

[alomerry]

✅ Checklist

• [X] I am using the latest version

🔎 Description

Concise Description

滚动条被白色的方块包起来，背景是黑色的，看起来怪怪的。。。

Expected behavior

滚动条不用改有白色框框包围

Steps to reproduce

Screenshots or Screen Recording (if possible)

📄 Environment info (npx vuepress info)

System:
    OS: macOS 12.0.1
    CPU: (8) arm64 Apple M1
    Memory: 100.36 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.13.0 - /usr/local/bin/node
    Yarn: 1.22.17 - /usr/local/bin/yarn
    npm: 8.1.0 - /usr/local/bin/npm
  Utilities:
    Git: 2.30.1 - /usr/bin/git
  Browsers:
    Chrome: 103.0.5060.53
    Edge: Not Found
    Firefox: Not Found
    Safari: 15.1
  npmPackages:
    @vuepress/bundler-vite: 2.0.0-beta.48 => 2.0.0-beta.48
    @vuepress/bundler-webpack: Not Found
    @vuepress/cli: 2.0.0-beta.48 => 2.0.0-beta.48
    @vuepress/client: 2.0.0-beta.48 => 2.0.0-beta.48
    @vuepress/core:  2.0.0-beta.48
    @vuepress/markdown:  2.0.0-beta.48
    @vuepress/plugin-active-header-links:  2.0.0-beta.48
    @vuepress/plugin-back-to-top:  2.0.0-beta.48
    @vuepress/plugin-container:  2.0.0-beta.48
    @vuepress/plugin-docsearch: Not Found
    @vuepress/plugin-external-link-icon:  2.0.0-beta.48
    @vuepress/plugin-git:  2.0.0-beta.48
    @vuepress/plugin-google-analytics:  2.0.0-beta.48
    @vuepress/plugin-medium-zoom:  2.0.0-beta.48
    @vuepress/plugin-nprogress:  2.0.0-beta.48
    @vuepress/plugin-palette:  2.0.0-beta.48
    @vuepress/plugin-prismjs:  2.0.0-beta.48
    @vuepress/plugin-pwa:  2.0.0-beta.48
    @vuepress/plugin-pwa-popup:  2.0.0-beta.48
    @vuepress/plugin-register-components: Not Found
    @vuepress/plugin-search: Not Found
    @vuepress/plugin-shiki: Not Found
    @vuepress/plugin-theme-data:  2.0.0-beta.48
    @vuepress/plugin-toc: Not Found
    @vuepress/shared:  2.0.0-beta.48
    @vuepress/theme-default:  2.0.0-beta.48
    @vuepress/utils:  2.0.0-beta.48
    vue: ^3.2.36 => 3.2.37
    vue-loader: Not Found
    vue-router:  4.0.16
    vuepress: 2.0.0-beta.48 => 2.0.0-beta.48
    vuepress-vite:  2.0.0-beta.48
    vuepress-webpack: Not Found

### 🔗 Reproduction link / repo:

_No response_

[rainbowatcher]

@Renovamen 你好，我试着修改了一下代码块的滚动条样式，下面是截图 接下来是hover状态的效果 你看这个效果是不是可以接受。