Ruling on adorning the bridal car with flowers

There is nothing wrong with adorning the bridal car with flowers on the wedding day, because the basic principle is that things are permissible, and this comes under the heading of things that bring joy to the bride and her husband and their families. But there should be no extravagance involved in that, because Allah, may He be exalted, says (interpretation of the meaning):

{and eat and drink, but be not excessive. Indeed, He likes not those who commit excess} [al-A‘raaf 7:31].

And Allah knows best.