Currently, if user clicks the mass mailing template (theme) and holds
the click while moving the mouse (as if performing drag and drop), a
weird white highlight appears on the preview of the template.
This commit fixes the behavior by setting appropriate background color
instead of the default one of drop-down item, when the template is
focused.
task-2812312
closesodoo/odoo#89893
X-original-commit: e49f55e6f34486f8425653323544838f1a9fbd38
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>