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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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Adding Classes

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About the <head>

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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).

Add External Stylesheets/Pens

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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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You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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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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About Packages

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.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <div class="impossible"></div>
!

CSS 

              
                $white: #ffffff;
$black: #444444;
$blue-gray: #b5c4d9;

*, *:before, *:after {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}


body {
  height: 100vh;
  width: 100vw;
  position: relative;
  z-index: 1;
  background: linear-gradient(-90deg, lighten($blue-gray, 10%) 15%, lighten($blue-gray, 5%) 100%);
}



div.impossible {
    width: 100vmin;
    height: 100vmin;
    top: -15vmin;
    left: 5vmin;
    //transform-origin: 46% 67%;
    //animation: rotatetriangle 20s linear infinite;
    position: relative;  
    display: flex;
    position: relative; 
    justify-content: center;
    align-items: center; 
    margin: 0 auto;
    background: 

   /* bottom-dark */ linear-gradient(60deg, $black 0vmin, $black 38vmin, transparent 38vmin) 20vmin 77vmin / 80vmin 7.5vmin no-repeat,

   /* bottom-mid */ linear-gradient(-120deg, lighten($black, 40%) 0vmin, lighten($black, 40%) 50vmin, transparent 50vmin) -9.5vmin 84.5vmin / 80vmin 7.5vmin no-repeat,

   /* right-light */ linear-gradient(60deg, transparent 18.5vmin, $white 18.5vmin, $white 25vmin, transparent 25vmin) 50vmin 25vmin / 50vmin 60vmin no-repeat,   
    linear-gradient(120deg, $white 0vmin, $white 3.5vmin, transparent 3.5vmin) 75vmin 85vmin / 10vmin 10vmin no-repeat,
      linear-gradient(-120deg, $white 0vmin, $white 3vmin, transparent 3vmin) 65vmin 85vmin / 10vmin 10vmin no-repeat,

   /* left-light */ linear-gradient(-60deg, transparent 18.5vmin, $white 18.5vmin, $white 25vmin, transparent 25vmin) 0vmin 25vmin / 50vmin 60vmin no-repeat,

    /* left-dark */ linear-gradient(-60deg, transparent 18.5vmin, $black 18.5vmin, $black 32vmin, transparent 32vmin) 0vmin 35vmin / 50vmin 50vmin no-repeat,

    /* right-mid */ linear-gradient(60deg, transparent 18.5vmin, lighten($black, 40%) 18.5vmin, lighten($black, 40%) 25vmin, transparent 25vmin) 46.5vmin 34vmin / 50vmin 58vmin no-repeat;
}

 @keyframes rotatetriangle {
   0% {
     transform: rotate(0deg);
   }
  100% {
     transform: rotate(360deg);
   }
}
!

JS 

              
                /* This entry for #divtober 2023 is for impossible. The Penrose Triangle is an impossible triangle that I first became fascinated by in the works of M. C. Escher.   */
!
999px

Console