Improve styling of progress bar on wp-admin/media-new.php.

props Ipstenu for initial patch.
fixes #28838.
Built from https://develop.svn.wordpress.org/trunk@29121


git-svn-id: http://core.svn.wordpress.org/trunk@28906 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't use box shadow focus styling for widget arrows, see #28267.

fixes #28834.
props nvwd.
Built from https://develop.svn.wordpress.org/trunk@29122


git-svn-id: http://core.svn.wordpress.org/trunk@28907 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use correct ID for plugin search input label.

Make the search button name and ID consistent with the ones in WP_List_Table::search_box().

props joedolson.
fixes #28856.
Built from https://develop.svn.wordpress.org/trunk@29123


git-svn-id: http://core.svn.wordpress.org/trunk@28908 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Themes: Don't set background color for the filter icon.

fixes #28860.

Built from https://develop.svn.wordpress.org/trunk@29124


git-svn-id: http://core.svn.wordpress.org/trunk@28909 1a063a9b-81f0-0310-95a4-ce76da25c4cd