Border radius with Box shadow css

I have box-shadow on form which stretches on whole screen and it worked perfectly until i added border-radius to form.

Code:

.customer-modal{
    box-shadow: 0px 0px 300px 900px rgba(0,0,0,0.75);
    background: whitesmoke;
    display: inline-block;
    width: 40vw; 
    padding-bottom: 60px;
}

Code with radius

.customer-modal{
    box-shadow: 0px 0px 300px 900px rgba(0,0,0,0.75);
    background: whitesmoke;
    display: inline-block;
    width: 40vw;
    padding-bottom: 60px;
    border-radius: 4%;
}

It looks like this:

How can i fix it so box shadow looks as it looked without border-radius?