[css] How to apply a CSS filter to a background image

All you actually need is "filter":

blur(«WhatEverYouWantInPixels»);"

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body {_x000D_
    color: #fff;_x000D_
    font-family: Helvetica, Arial, sans-serif;_x000D_
}_x000D_
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#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_
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    /* START */_x000D_
    /* START */_x000D_
    /* START */_x000D_
    /* START */_x000D_
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    /* You can adjust the blur-radius as you'd like */_x000D_
    filter: blur(3px);_x000D_
}
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<div id="background"></div>_x000D_
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<p id="randomContent">Lorem Ipsum</p>
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