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HTML

              
                <div class="page-head--masthead">
</div>
              
            
!

CSS

              
                // Blurground:
// Create a blurry background image 
// using radial gradients as "pixel 
// blobs". Inspired by Harry Roberts'
// blog post: 
// https://csswizardry.com/2016/10/improving-perceived-performance-with-multiple-background-images
// WARNING: This is ridiculous

// 1. THE SOURCE IMAGE
// First you need to reduce your source 
// image to the desired size, using 
// Photoshop or similar. In this example 
// I've reduced this image: 
// https://csswizardry.com/img/css/masthead-large.jpg
// to 8x4 pixels. Use Photoshop's 
// inkdropper tool to record the colour 
// of each pixel, and list them in a
// a Sass list, like this:

$myColours: #9EA0A3, #9C9A97, #362F29, #15100D, #271E17, #241C17, #040201, #1C1C1C, #A9ABAC, #999999, #190E03, #000000, #6A4D44, #533C37, #000000, #141111, #AC9479, #746454, #0A0300, #3B3134, #715A60, #5C453E, #15100C, #0D0D0D, #A37A52, #49301A, #0D0D0D, #493B3A, #584D51, #624638, #1A0C06, #2A2A2C;

// I guess this bit could be automated
// using Node or ImageMagick or 
// something? I'll leave that job to
// someone smarter than me...

// Blurground will turn each pixel into 
// a radial gradient, or blob. So in 
// this example we'll end up with an 
// 8x4 grid of blobs.

// 2. THE FUNCTION
// $rowLength = number of blobs in width
// $columnLength = num. blobs in height
// $colours = your Sass list of colours
@function blurground($rowLength, $columnLength, $colours) {
  
  // Determines the size of each grid square
  $blobWidth: 100%/$rowLength;
  $blobHeight: 100%/$columnLength;
  
  // Centre-align each blob within its grid square
  $xOffset: $blobWidth/2;
  $yOffset: $blobHeight/2;
  
  // Size determines how much the blobs 
  // overlap: if size==width, no overlap
  $xSize: $blobWidth*2;
  $ySize: $blobHeight*2;
  
  // An empty string which will contain our CSS
  $result: "";
  
  // This code loops through each colour
  // in the list, creating a radial 
  // gradient (or blob) for each. We
  // know what number blob we're on, and
  // the size of our grid, so calculatin
  // calculating each blob's x & y
  // co-ordinates is just a math problem
  @for $currentBlob from 1 through length($colours) {
    
    // What row are we on? 
    $row: ceil($currentBlob/$rowLength);
    $const: $row - 1;
    
    $xPosition: (($currentBlob - ($rowLength * $const)) * $blobWidth) - $xOffset;
    $yPosition: ($blobHeight * $row) - $yOffset;
    $string: "radial-gradient(ellipse #{$xSize} #{$ySize} at #{$xPosition} #{$yPosition}, #{rgba(nth($colours,$currentBlob),1)}, #{rgba(nth($colours,$currentBlob),0)})";
    $separator: "";
    @if ($currentBlob != 1) {
      $separator: ",";
    }
    $result: $result + $separator + $string;
  }
  
  @return unquote($result);
}

// 3. USAGE
// That's it! Here's how you'd use 
// the function:
.page-head--masthead {
  background-image: blurground(8,4,$myColours);
  height: 426px;
}

// Thanks for reading!

// DISCLAIMER:
// This is just a thought experiment;
// I would never suggest anyone use
// this code in production. The CSS
// it produces could potentially be 
// much heavier than the source image, 
// therefore entirely missing the point 
// of Harry's initial blog post. It was
// fun to mess around with though :D
              
            
!

JS

              
                
              
            
!
999px

Console