Bug 10777: (follow-up) improve CSS3 for Zebra-striping report email output

Bug 10777: (follow-up) improve CSS3 for Zebra-striping report email output

This patch improves the CSS used to attempt to Zebra-stripe the
output of emailed reports.  This will work with some email clients,
but other email clients (e.g., Gmail) don't handle style elements in the
body or head element.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 26cdaaae777dd21314df90177fe070730575fb85)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit d726bf355cc7daec12ac10adfad1f06be4fcc568)