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HTML

              
                <canvas id="stage"></canvas>
              
            
!

CSS

              
                html, body {
   display: block; 
   overflow: hidden; 
   position: relative;
   min-height: 100vh; 
   margin: 0; 
   padding: 0; 
   background: #0c0c0c url( 'https://wallpaper-house.com/data/out/10/wallpaper2you_401725.png' ) center bottom no-repeat;
   background-size: cover;
}

canvas {
   display: block; 
   background-color: transparent; 
   margin: 0; 
   padding: 0;
   opacity: 1; 
}

              
            
!

JS

              
                // global  canvas data 
var canvas  = document.getElementById( "stage" );
var context = canvas.getContext( "2d" );
var width   = window.innerWidth  || 0; 
var height  = window.innerHeight || 0; 
var total   = 600; 
var flakes  = []; 

// update dimentions 
function resize( e )
{
   width  = window.innerWidth || 0; 
   height = window.innerHeight || 0; 
   canvas.width  = width; 
   canvas.height = height; 
   canvas.style.width  = width + 'px';
   canvas.style.height = height + 'px';
}; 

// make new flakes 
function create()
{
   for( var i = 0; i < total; ++i ) 
   {
      flakes.push( new Flake() );  
   }
}; 

// main animation loop 
function loop() 
{
   requestAnimationFrame( loop ); 
   context.clearRect( 0, 0, width, height ); 
   
   for( var i = 0; i < flakes.length; ++i ) 
   {
      flakes[ i ].update(); 
      flakes[ i ].draw(); 
   }
};

// get rand int between min/max 
function rand( min, max, round ) 
{
   if( round ) 
   {
      return Math.floor( Math.random() * ( max - min + 1 ) ) + min; 
   }
   return Math.random() * ( max - min ) + min;
};

// snow flake object 
var Flake = (function() 
{
   var FlakeFactory = function() 
   {
      this.x = 0;
      this.y = 0;
      this.factor = 0;
      this.count = 0;
      this.speed = 5; 
      this.size = 5;
      this.wind = 2; 
      this.init(); 
   };
   
   FlakeFactory.prototype = {
      constructor: FlakeFactory, 
      
      init: function() 
      {
         this.x = rand( 0, width, true ) - ( this.wind * 200 );
         this.y = rand( -height, -10, true );
         this.factor = rand( 0.2, 1.0 );
         this.count = rand( 0, 1000, true );
         // this.speed = this.speed * this.factor;
      }, 
      
      update: function() 
      {
         
         this.x += this.wind + Math.cos( this.count / 20 ); 
         this.y += this.factor * ( Math.sin( this.count / 100 ) + this.speed ); 

         if( this.y > height )
         {
            this.init(); 
         }
         this.count++; 
      }, 
      
      draw: function() 
      {
         var size = this.size * this.factor; 
         var grad = context.createRadialGradient( this.x, this.y, 0, this.x, this.y, size );
         
         if ( this.factor > .9 ) { // blury
            size = this.size * ( this.factor * 6 ); 
            grad = context.createRadialGradient( this.x, this.y, 0, this.x, this.y, size );
            grad.addColorStop( 0, 'rgba( 250, 250, 255, .1 )' );
            grad.addColorStop( .5, 'rgba( 250, 250, 255, .05 )' );
            grad.addColorStop( 1, 'rgba( 250, 250, 255, 0 )' );
         } 
         else if ( this.factor > .8 ) { // blury
            size = this.size * ( this.factor * 2 ); 
            grad = context.createRadialGradient( this.x, this.y, 0, this.x, this.y, size );
            grad.addColorStop( 0, 'rgba( 250, 250, 255, .2 )' );
            grad.addColorStop( .6, 'rgba( 250, 250, 255, .08 )' );
            grad.addColorStop( 1, 'rgba( 250, 250, 255, 0 )' );
         }  
         else { // sharp 
            grad.addColorStop( 0, 'rgba( 250, 250, 255, 1 )' );
            grad.addColorStop( .5, 'rgba( 250, 250, 255, .8 )' );
            grad.addColorStop( 1, 'rgba( 250, 250, 255, 0 )' );
         }
      
         context.beginPath();
         context.fillStyle = grad;
         context.arc( this.x, this.y, size, 0, 2 * Math.PI, false );
         context.fill();
         context.closePath();
      }, 
      
   }; 
   return FlakeFactory; 
})(); 


// init 
context.imageSmoothingEnabled = true; 
context.globalCompositeOperation = "lighten"; 
window.addEventListener( "resize", resize );  
resize(); 
create(); 
loop(); 
              
            
!
999px

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