Notices: compact inline notices have too much contrast in certain areas

[davewhitley]

Steps to reproduce

1. Starting at URL:https://wpcalypso.wordpress.com/plugins/manage/[site]

To quote @mtias in #17796

...compact-inline which has been used to seek a more subdued approach to signaling information and is likely to clash a lot more.

Compact notices are now very distinctive and they were not before:

Suggestions

We need to retain contrast of the text so that it passes WCAG.

We could remove the background and do something like:

This issue doesn't seem to be as simple as diverging compact inline notices and global notices. For example, this compact inline notice should retain its dark contrast style:

[stale]

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