[wp-trac] [WordPress Trac] #46015: Remove any CSS related to Internet Explorer 6 – 8

[WordPress Trac]

#46015: Remove any CSS related to Internet Explorer 6 – 8
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 Reporter:  afercia         |      Owner:  (none)
     Type:  defect (bug)    |     Status:  new
 Priority:  normal          |  Milestone:  Awaiting Review
Component:  Administration  |    Version:
 Severity:  normal          |   Keywords:
  Focuses:  performance     |
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 Splitting this out from #46003.

 More than one year ago, with the 4.8 release, WordPress
 [https://make.wordpress.org/core/2017/04/23/target-browser-coverage/
 officially ended support for Internet Explorer versions 8, 9, and 10].

 However, the WordPress admin CSS is still targeting old IE versions, even
 IE 6. It is true that in the admin some of these rules are only served to
 old IE versions via conditional comments. There are many other rules
 targeting IE 7 and IE 8 polluting styesheets served to all browsers
 though.

 Not to mention the majority of the bundled themes. As far as I can tell,
 Twenty Nineteen is the first bundled theme to not use conditional
 comments.

 At the very least, I'd like to propose to remove any admin CSS targeting
 IE 6 – 8. That would require to:
 - remove `wp-admin/css/ie.css`
 - remove the conditional comments
 - remove any CSS rule that use selectors with `.ie7` and `.ie8`.
 - check if anything else is needed

 As mentioned in #46003, some of the related CSS is served also in the
 front end. For example, the CSS related to the admin bar, when users are
 logged in, and the media views, when enqueued in the front end.

 It would be great to consider to do the same also for the JavaScript part.
 That would certainly be a bit more complicated and I guess it needs to be
 considered separately. Instead, the CSS part seems easy enough to address.

 /Cc @swissspidy

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Ticket URL: <https://core.trac.wordpress.org/ticket/46015>
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