All you actually need is "filter":
blur(«WhatEverYouWantInPixels»);"
body {_x000D_
color: #fff;_x000D_
font-family: Helvetica, Arial, sans-serif;_x000D_
}_x000D_
_x000D_
#background {_x000D_
background-image: url('https://cdn2.geckoandfly.com/wp-content/uploads/2018/03/ios-11-3840x2160-4k-5k-beach-ocean-13655.jpg');_x000D_
background-repeat: no-repeat;_x000D_
background-size: cover;_x000D_
width: 100vw;_x000D_
height: 100vh;_x000D_
overflow: hidden;_x000D_
position: absolute;_x000D_
top: 0;_x000D_
left: 0;_x000D_
z-index: -1;_x000D_
_x000D_
/* START */_x000D_
/* START */_x000D_
/* START */_x000D_
/* START */_x000D_
_x000D_
/* You can adjust the blur-radius as you'd like */_x000D_
filter: blur(3px);_x000D_
}
_x000D_
<div id="background"></div>_x000D_
_x000D_
<p id="randomContent">Lorem Ipsum</p>
_x000D_