1. Remove unnecessary `btn-link` `muted` classes
* Link is link, button is button, I can't see a real requirement to make
a button like a link.
* If anyone insists, please help to show me real example from modern
frameworks / websites, how and why they do so.
* No need to duplicate a lot of class names on similar elements
* Declare styles clearly, for example, `markdown-toolbar` itself should
have `display: flex`, but not use `gt-df` to overwrite the `display:
block`.
2. Remove unnecessary `role` attribute
* https://github.com/github/markdown-toolbar-element/issues/70
* The `markdown-toolbar-element` does want to add `role=button`, but
there is a bug.
* So we do the similar thing as upstream does (add the role by JS),
until they fix their bugs.
3. Indent `markdown-switch-easymde` (before it doesn't have a proper
indent)
Screenshot:
The completion popup now behaves now much more as expected than before
for the raw textarea:
- You can press <kbd>Tab</kbd> or <kbd>Enter</kbd> once the completion
popup is open to accept the selected item
- The menu does not close automatically when moving the cursor
- When you delete text, previously correct suggestions are shown again
- If you delete all text until the opening char (`@` or `:`) after
applying a suggestion, the popup reappears again
- Menu UI has been improved
<img width="278" alt="Screenshot 2023-04-07 at 19 43 42"
src="https://user-images.githubusercontent.com/115237/230653601-d6517b9f-0988-445e-aa57-5ebfaf5039f3.png">
