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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

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HTML 

              
                
<div class="ball">
  <div class="halo"></div>
  <div class="halo"></div>
  <div class="halo"></div>
</div>
!

CSS 

              
                :root {
  --mouse-x;
  --mouse-y;
  --scale;
  --radius: 40px;
  --factor: 1;
}

.ball {
  width: var(--radius);
  height: var(--radius);
  background: #D92659;
  border-radius: 50%;
  position:absolute;
/* use calc() and the CSS variables created above to center the ball around the mouse position.  */
  transform: translate(calc(var(--mouse-x) * 1px - var(--radius)/2),calc(var(--mouse-y) * 1px - var(--radius)/2));
}

.halo {
  width: var(--radius);
  height: var(--radius);
  background: rgb(114, 61, 83);
  border-radius: 50%;
  position:absolute;
  opacity: .15;
/*   filter: blur(var(--factor)); */
  transform: scale(calc(var(--scale) * var(--factor)));
 
}

.halo:nth-of-type(1) {
  --factor: .3;
}

.halo:nth-of-type(2) {
  --factor: 0.5;
}

.halo:nth-of-type(3) {
  --factor: .9;
}

body {
  background: #070611;
  font-family: Verdana, sans-serif;
}

p {
  color: whitesmoke;
  width: 400px;
  top: 10px;
  left: 10px;
  position:absolute;
}
!

JS 

              
                var [xpos,targetX,ypos,targetY, velX, velY] = [0,0,0,0,0,0];

const docStyle = document.documentElement.style;
const drag = 0.8;
const strength = 0.12;

function springItOn() {

  var diffX = targetX - xpos; 
  diffX *= strength;
  velX *=drag;
  velX += diffX;
	xpos += velX;
  
  var diffY = targetY - ypos; 
  diffY *= strength;
  velY *=drag;
  velY += diffY;
	ypos += velY;
  
  //apply the newly calculated positions via CSS custom properties each frame. SO FANCY
  docStyle.setProperty('--mouse-x', xpos);
  docStyle.setProperty('--mouse-y', ypos);
  
  //set the halo scale property baesd on some arbitrary math for kicks
  docStyle.setProperty('--scale', (velY + velX)*strength);

  requestAnimationFrame(springItOn);
}

springItOn();

//update the target position based on where the mouse is
 document.addEventListener('mousemove', (e) => {
  targetX = e.clientX;
  targetY = e.clientY;
});
!
999px

Console