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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-.

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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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HTML 

              
                <div id="app">
	<div class="item item-one">
		<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-moon">
    <path d="M21 12.79A9 9 0 1 1 11.21 3 7 7 0 0 0 21 12.79z"/>
</svg>
	</div>
	<div class="item item-two">
		<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-sun">
    <circle cx="12" cy="12" r="5"/>
    <path d="M12 1v2M12 21v2M4.22 4.22l1.42 1.42M18.36 18.36l1.42 1.42M1 12h2M21 12h2M4.22 19.78l1.42-1.42M18.36 5.64l1.42-1.42"/>
</svg>
	</div>
	<div class="item item-three">
		<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-star">
    <path d="M12 2l3.09 6.26L22 9.27l-5 4.87 1.18 6.88L12 17.77l-6.18 3.25L7 14.14 2 9.27l6.91-1.01L12 2z"/>
</svg>

	</div>
	<div class="item item-four">
		<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-activity">
    <path d="M22 12h-4l-3 9L9 3l-3 9H2"/>
</svg>

	</div>
</div>
!

CSS 

              
                body, html {
  height: 100%;
  width: 100%;
  margin: 0;
  padding: 0;
}

body {
  background: #feffdf;
  display: flex;
  justify-content: center;
  align-items: center;
	font-family: monospace;
}

#app {
	display: flex;
	flex-wrap: wrap;
	flex-direction: row;
	justify-content: center;
	align-items: center;
  height: 87vh;
  width: 46vh;
  transform: scale(0.8);
  border-radius: 2rem;
  background-color: #ef5a5a;
	color: #fff;
  box-shadow: 0px 2vh 10vh rgba(0,0,0,.3);
  overflow: hidden;
  border: 1vh solid #F0F0F0;
	box-sizing: border-box;
	padding: 20px;
}

.item {
	margin: 20px;
	flex: 0 0 35%;
	
	svg {
		width: 100%;
		height: auto;
	}
	
	&-one {
		transform: rotate(calc(var(--x) * 360deg));
	}
	
	&-two {
		transform: scale(calc(calc(var(--x) * 0.5) + 1));
	}
	
	&-three {
		opacity: calc(var(--x) + 1);
	}
	
	&-four {
		transform: translateX(calc(var(--x) * 10px));
	}
}
!

JS 

              
                const frame = document.querySelector('#app');
let raf; 

document.addEventListener('mousemove', (e) => {
  raf = raf || requestAnimationFrame(() => update(e));
});

function update(e){
	const x =  ((e.clientX / window.innerWidth) - 0.5) * 2;
  frame.style.setProperty('--x', x );
  raf = null;
}
!
999px

Console