Improve blockquotes
Currently, the render doesn't draw anything behind the quoted text, just adds some padding behind it.
| GitHub | GitLab | Marknote-git |
| ---------- | ------ | ------------- |
| {width=186 height=139} | {width=186 height=139} | {width=225 height=138} |
For the reference: [markdownguide](https://www.markdownguide.org/basic-syntax/#blockquotes-1).
issue