When saving a new style, we get a general message instead of an actual reason of an error.

[sEver]

I was saving a style and got the "There's an error with your CSS code, please review it" message.

Since I had no idea what the error could be. I opened devtools, retried the save action and inspected the API response to the save request.
The response was

style_code-looks unintentionally global. Please read https://github.com/JasonBarnabe/stylish/wiki/Preventing-global-styles .

Since that response and the cause of error is known and provided, it should be included in the error popup in the UI.
Additionally, the error should not disappear on a timer, so the user has time to read it and click/copy the link.