CSS backdrop filter?

Hello, I want the background to be dark and fill the entire background. However, I'm having trouble with the filter not working for the bottom part of the image (see image). This is probably because the body ends before it. Does anyone have a fix for this?

CSS:

 body{  font-family: 'Gill Sans', 'Gill Sans MT', Calibri, 'Trebuchet MS', sans-serif;  height: 100%;  width: 100%;  margin: 0;  padding: 0;  background-image: url(moviebackground.jpg);  backdrop-filter: brightness(10%);  background-size: cover;  background-repeat: no-repeat; }