Since the redesign of the default theme [1], `website_forum` needed to be fine-tuned in order to fit with the other website modules. This commit adapts the sidebar to maintain consistency with the other website modules. [1]: https://github.com/odoo/odoo/pull/120302 task-3559011 Part of task-3097005 closes odoo/odoo#139003 Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>