background image greyscale filter while foreground is still in colour

HTML

<div class='demo-bg flex-center'>
  <div class='demo-bg-inner'>some inner text</div>
</div>

CSS

.flex-center {
	display: flex;
	align-items: center;
	justify-content: center;
}
.demo-bg {
  position: relative;
  width:100%;
  height:400px;  
}
.demo-bg::before {
  content: "";
  position: absolute;
  top: 0; 
  left: 0;
  width: 100%; 
  height: 100%;
  background-image: url(https://kruxor.com/images/pexels-photo-546819.jpeg);
  filter: grayscale(100%);
}
.demo-bg-inner {
  position: relative;
  color:red;
  font-size:32px;
  font-weight:bold;
}