Lightning modal external page scroll bar

Hi I am working on a lightning component to show banks checkout page in a modal popup. There is no customization of the external page. The page is showing double scroll bars. One for the external page and one for the body of the popup.

I have tried to add this css

.THIS .slds-modal__header {
    border-bottom:3px solid #FFA000;
    height: 10vh;
    margin: 0;
    padding: 0;
}

.THIS .slds-modal__content {
    overflow-y: auto;
}

.THIS .slds-modal__body {
    height: 80vh;
}

.THIS .slds-modal__footer {
    border-top:3px solid #FFA000;
    height: 10vh;
    margin: 0;
    padding: 10px;
}

But the external page is still taking long and not showing in the body area of the popup. Can we resize the body area to show the external page in the body area only with the scroll bar.

Thanks