Using important is only going to fix the problem if you have defined a style for that element. For example, if you have not defined a border then the client wil

Using important is only going to fix the problem if you have defined a style for that element. For example, if you have not defined a border then the client will still be able to add one. Most sites use iframe for embeded widgets for this reason. I think Stripe's checkout doesn't use iframe. They just define every single style with very specific rules. From what I remember.