Before this commit, background images were not centered by default. It was especially annoying on mobile device. We created a new class to center background image and we added it on all the snippets with a background image except those with a parallax effect because they already have a background-position in inline style. task-2318526 closes odoo/odoo#60430 Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>