[FIX]website: fix problem of hide snippet grid while it is on low resolu...

Task: https://www.odoo.com/web#id=10387&view_type=form&model=project.task&menu_id=3942&action=327
Pad: https://pad.odoo.com/p/r.upol57weALe65Qfd
what is purpose of add + sign ? and why change margin-top ?