Prior to this commit it was not possible to detect/use the default border-color in within the 'primary_variables` bundle. This commit define a new `$o-border-color` variable to be used in BS overrides and by components/functionalities that need it (eg. dark-mode) task-3012970 X-original-commit: 29cd4ad3601cd6d3d86c8eaa747ddff600061c00 Part-of: odoo/odoo#103118