Update error screens with the new visual design:

* Bring in new styles for backgrounds/text/link/borders/buttons
* Switch to device-width for the viewport and tweak margins etc so the layout works nicely on all device sizes

Fixes #25956, props johnbillion.


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git-svn-id: http://core.svn.wordpress.org/trunk@26204 1a063a9b-81f0-0310-95a4-ce76da25c4cd