Before BS4 migration, Odoo was not very consistent and used mainly btn-sm buttons and btn-xs buttons. We took advantage of the fact BS4 removed the btn-xs class to convert our btn-sm to standard btn and our btn-xs to standard btn-sm. While this is perfect in theory, the new btn-sm class does not generated small enough design for us. This commit changes the BS4 standard style for our website, making btn-sm smaller.