Keyboard navigation friendliness for themes.php.

props matveb, azaozz, jorbin.
see #26527.

Built from https://develop.svn.wordpress.org/trunk@26922


git-svn-id: http://core.svn.wordpress.org/trunk@26803 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix another CSS clashing on the Network Themes page.

props SergeyBiryukov.
see #26513 for trunk.
Built from https://develop.svn.wordpress.org/trunk@26923


git-svn-id: http://core.svn.wordpress.org/trunk@26804 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Pass the $user_id to the `admin_color_scheme_picker` hook for context. props nacin. see #26607 for trunk.

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git-svn-id: http://core.svn.wordpress.org/trunk@26805 1a063a9b-81f0-0310-95a4-ce76da25c4cd