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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

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

!
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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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

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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 Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

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HTML 

              
                <div id="scene"></div>
<details class="settings-panel">
  <summary class="settings-panel-title">Settings</summary>
  <div id="settings"></div>
  <button id="print">Print to console</button>
</details>

<template id="range-setting-template">
  <label class="setting">{id}: <span id="{id}-value">{value}</span>
    <br />
    <input id="{id}-input" type="range" min="{min}" max="{max}" value="{value}" />
  </label>
</template>

<template id="color-setting-template">
  <label class="setting">{id}: <span id="{id}-value">{value}</span>
    <br />
    <input id="{id}-input" type="color" value="{value}" />
  </label>
</template>
!

CSS 

              
                :root {
  --rotation: 90deg;
  --container-width: 300px;
  --container-height: 50px;
  --element-width: 96%;
  --element-height: 101%;
  --element-bottom: -30%;
  --element-right: -24%;
  --outline-width: 1px;
  --body-background-color: #0a061e;
  --border-top-color: #ce92af;
  --border-right-color: #00ffcc;
}


body {
  margin: 0;
  overflow: hidden;
  background: var(--body-background-color);
  font-family: "Operator Mono", menlo, monaco, monospace;
  font-size: 14px;
  color: white;
}

.settings-panel {
  /* Remove this to enter adjustment mode */
  display: none;
  position: absolute;
  max-width: 200px;
  max-height: 435px;
  overflow: auto;
  padding: .5em;
  background: #00000099;
  border-radius: 6px;
}

.settings-panel-title {
  cursor: pointer;
}

.settings-panel[open] .settings-panel-title {
  cursor: default;
}

#settings {
  position: relative;
  z-index: 2;
}

.setting {
  display: block;
  margin-bottom: .5em;
}

.setting:first-of-type {
  margin-top: 1em;
}

#scene {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

#scene div {
  width: var(--container-width);
  height: var(--container-height);
  border-top: var(--outline-width) solid var(--border-top-color);
  border-right: var(--outline-width) solid var(--border-right-color);
  position: relative;
  border-radius: 100%;
  transform: translateZ(0) rotate(var(--rotation));
  animation:
    portal-width 2.5s infinite,
    portal-height 10s infinite;
}

#scene div div {
  width: var(--element-width);
  height: var(--element-height);
  position: absolute;
  bottom: var(--element-bottom);
  right: var(--element-right);
  animation: portal-element 2.5s infinite linear;
}

@keyframes portal-width {
  50% {
    width: 100px;
  }
}

@keyframes portal-height {
  50% {
    height: 300px;
  }
}

@keyframes portal-element {
  50% {
    width: 102%;
  }
}
!

JS 

              
                const getNestedMarkup = (tagName, amount) => {
  return [
    Array(amount).fill(`<${tagName}>`).join(''),
    Array(amount).fill(`</${tagName}>`).join('')
  ].join('')
}

const query = document.querySelector.bind(document)

const setCSSProperty = (key, value, scope = window.document.documentElement) => {
  scope.style.setProperty(key, value)
}

const renderTemplate = (template, data) => {
  Object.keys(data).forEach(key => {
    const pattern = new RegExp(`{${key}}`, 'g')
    template = template.replace(pattern, data[key])
  })
  return template
}

const settings = [{
  id: 'rotation',
  type: 'range',
  min: -360,
  max: 360,
  value: 90,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}deg`
  }
}, {
  id: 'container-width',
  type: 'range',
  max: 1000,
  value: 300,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}px`
  },
}, {
  id: 'container-height',
  type: 'range',
  max: 1000,
  value: 50,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}px`
  }
}, {
  id: 'element-width',
  type: 'range',
  max: 200,
  value: 96,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}%`
  }
}, {
  id: 'element-height',
  type: 'range',
  max: 200,
  value: 101,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}%`
  }
}, {
  id: 'element-bottom',
  type: 'range',
  min: -100,
  max: 100,
  value: -30,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}%`
  }
}, {
  id: 'element-right',
  type: 'range',
  min: -100,
  max: 100,
  value: -24,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}%`
  }
}, {
  id: 'elements',
  type: 'range',
  min: 1,
  max: 100,
  value: 100,
  fn() {
    const container = query('#scene')
    container.innerHTML = getNestedMarkup('div', +this.value)
  }
}, {
  id: 'outline-width',
  type: 'range',
  min: 1,
  max: 50,
  value: 1,
  hasCSSProperty: true,
  get formattedValue() {
    return `${this.value}px`
  }
}, {
  id: 'body-background-color',
  type: 'color',
  value: '#0a061e',
  hasCSSProperty: true
}, {
  id: 'border-top-color',
  type: 'color',
  value: '#ce92af',
  hasCSSProperty: true
}, {
  id: 'border-right-color',
  type: 'color',
  value: '#00ffcc',
  hasCSSProperty: true
}]

const settingTemplates = {
  range: query('#range-setting-template').innerHTML,
  color: query('#color-setting-template').innerHTML
}

const applySetting = (setting) => {
  const currentValue = setting.formattedValue || setting.value
  query(`#${setting.id}-value`).innerText = currentValue
  if (setting.hasCSSProperty) {
    setCSSProperty(`--${setting.id}`, currentValue)
  }
  if (setting.fn) {
    setting.fn(currentValue)
  }
}

const renderSettings = () => {
  const renderedSettings = settings
    .map(setting => {
      const template = settingTemplates[setting.type]
      return renderTemplate(template, setting)
    })
    .join('')

  query('#settings').innerHTML = renderedSettings
  settings.forEach(applySetting)

  query('#print').addEventListener('click', () => {
    const settingsText = JSON.stringify(settings, null, 2)
    console.log('const settings =', settingsText)

    const variablesText = query('html').style.cssText
      .split(';')
      .map(v => ` ${v}`)
      .join(';\n')
      .trim()
    console.log(':root {\n', variablesText, '\n}')
  })
}

const listenSettings = () => {
  settings.forEach(setting => {
    query(`#${setting.id}-input`).addEventListener('input', e => {
      setting.value = e.currentTarget.value
      applySetting(setting)
    })
  })
}

const animateRotation = (increment, interval) => {
  const rotation = settings.find(s => s.id === 'rotation')
  return setInterval(() => {
    rotation.value += increment
    applySetting(rotation)
  }, interval)
}

renderSettings()
listenSettings()
animateRotation(0.01, 1000 / 60)
!
999px

Console