Bug 29244: Move message inside dialog and remove width

Bug 29244: Move message inside dialog and remove width

This patch moves the message css rules inside the dialog ruleset to
clarify their intention and removes the width so it inherits from the
dialog class.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit cde0653deb322c749b6d43d1d67ff38b0d573ab6)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>