Rendered checkboxes in post content slightly off

## Problem
The checkboxes rendered by the [Discourse checklist rendering plugin](https://github.com/discourse/discourse-checklist) by writing down `[]` or `[x]` in the markup are slightly off.


## Workaround
```css
/* Fix DMT#15: Checkboxes slightly off */
.contents span.chcklst-box::before {
display: inline-flex;
margin-right: 0.1rem;
margin-bottom: 0.1rem;
}
```

Thank you in advance for your attention.

No theme file or test is named in the issue. Start by locating the stylesheet that controls post-content checklist boxes, compare the rendering with the supplied workaround, and verify visually that unchecked and checked boxes align correctly without the workaround being needed.

Written by the indexing model from the issue text.