Github-styled alerts padding

The padding issue with [`marked-alert`](https://github.com/bent10/marked-extensions/tree/main/packages/alert) are fixed (ref: https://github.com/sindresorhus/github-markdown-css/issues/110), so it's time to remove host style workarounds.