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HTML

About HTML Preprocessors

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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HTML 

              
                	<header>
    <div class="container">
     <h1>HTML Ipsum Presents</h1>
      <p class="header-description">
        hogehoge
      </p>
    </div>
  </header>
  <main>
    <div class="container">
      <section id="example">
    

<p><strong>Pellentesque habitant morbi tristique</strong> senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. <em>Aenean ultricies mi vitae est.</em> Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, <code>commodo vitae</code>, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. <a href="#">Donec non enim</a> in turpis pulvinar facilisis. Ut felis.</p>

<h2>Header Level 2</h2>

<ol>
   <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
   <li>Aliquam tincidunt mauris eu risus.</li>
</ol>

<blockquote><p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus magna. Cras in mi at felis aliquet congue. Ut a est eget ligula molestie gravida. Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis elit sit amet quam. Vivamus pretium ornare est.</p></blockquote>

<h3>Header Level 3</h3>

<ul>
   <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
   <li>Aliquam tincidunt mauris eu risus.</li>
</ul>

<pre><code>
#header h1 a {
  display: block;
  width: 300px;
  height: 80px;
}
</code></pre>
<ul>
   <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
   <li>Aliquam tincidunt mauris eu risus.</li>
   <li>Vestibulum auctor dapibus neque.</li>
</ul>
         <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus</p><ul>
   <li>Morbi in sem quis dui placerat ornare. Pellentesque odio nisi, euismod in, pharetra a, ultricies in, diam. Sed arcu. Cras consequat.</li>
   <li>Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus.</li>
   <li>Phasellus ultrices nulla quis nibh. Quisque a lectus. Donec consectetuer ligula vulputate sem tristique cursus. Nam nulla quam, gravida non, commodo a, sodales sit amet, nisi.</li>
   <li>Pellentesque fermentum dolor. Aliquam quam lectus, facilisis auctor, ultrices ut, elementum vulputate, nunc.</li>
</ul>
            <form action="#" method="post">
    <div>
         <label for="name">Text Input:</label>
         <input type="text" name="name" id="name" value="" tabindex="1" />
    </div>

    <div>
         <h4>Radio Button Choice</h4>

         <label for="radio-choice-1">Choice 1</label>
         <input type="radio" name="radio-choice-1" id="radio-choice-1" tabindex="2" value="choice-1" />

     <label for="radio-choice-2">Choice 2</label>
         <input type="radio" name="radio-choice-2" id="radio-choice-2" tabindex="3" value="choice-2" />
    </div>

  <div>
    <label for="select-choice">Select Dropdown Choice:</label>
    <select name="select-choice" id="select-choice">
      <option value="Choice 1">Choice 1</option>
      <option value="Choice 2">Choice 2</option>
      <option value="Choice 3">Choice 3</option>
    </select>
  </div>

  <div>
    <label for="textarea">Textarea:</label>
    <textarea cols="40" rows="8" name="textarea" id="textarea"></textarea>
  </div>

  <div>
      <label for="checkbox">Checkbox:</label>
    <input type="checkbox" name="checkbox" id="checkbox" />
    </div>

  <div>
      <input type="submit" value="Submit" />
    </div>
</form>
  <button id="mode-toggler" class="btn">
    Turn on Javascript 🌓
  </button>
!

CSS 

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

body {
    margin: 0;
    font-size: 18px;
    width: 100vw;
    line-height: 1.55;

}

header {
    padding-top: 60px;
    padding-bottom: 30px;
}

h1 {
    margin: 0;
    font-size: 64px;
    line-height: 1;
}

h2 {
    display: inline-block;
    position: relative;
    margin: 0 0 20px 0;
    font-size: 32px;
    line-height: 1;
}

h2:before {
    content: '';
    position: absolute;
    bottom: 0;
    right: 0;
    height: 6px;
    width: 72px;
    background-color: #3bc4fb;
    z-index: -1;
}

h3 {
    margin: 0;
    font-size: 20px;
}

main p {
    margin: 0 0 15px 0;
    max-width: 640px;
}

.header-description {
    margin: 20px 0 0 0;
    font-weight: 500;
    font-size: 16px;
    letter-spacing: .5px;
    font-style: italic;
}

main {
    padding-top: 100px;
}

section {
    padding-bottom: 100px;
    margin-bottom: -30px;
}

footer {
    padding-top: 15px;
    padding-bottom: 15px;
}

.footer-copyright {
    margin: 0;
    font-size: 14px;
    font-weight: 500;
}

.footer-copyright a {
    color: inherit;
}

#mode-toggler {
    position: fixed;
    bottom: 30px;
    right: 30px;
    font-size: 22px;
    padding: 15px 30px;
    border-radius: 50px;
    letter-spacing: .5px;
    font-weight: 700;
    border: 0;
}

.btn {
    display: inline-block;
    cursor: pointer;
    padding: 8px 16px;
    border: 2px solid #3bc4fb;
    font-weight: 600;
    text-transform: uppercase;
    font-size: 18px;
    line-height: 1;
    color: inherit;
    background-color: transparent;
    text-decoration: none;
    white-space: nowrap;
    user-select: none;
    background-color: #3bc4fb;
    transition: all .15s ease;
}

.btn:hover {
    background-color: #3bc4fb;
}

.btn:focus {
    outline: none;
}

.container {
    padding-left: 15px;
    padding-right: 15px;
    margin-left: auto;
    margin-right: auto;
    width: 100%;
    max-width: 830px;
}

pre {
    margin: 0 0 30px -9999px;
    padding: 30px 0 30px 9999px;
    -ms-overflow-style: scrollbar;
}

code {
    font-size: 14px;
    line-height: 1.8;
    display: block;
    overflow-x: auto;
    font-family: SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
}

.contacts-btns {
    padding: 0 0 30px 0;
    margin: -10px;
    display: flex;
    flex-flow: row wrap;
    align-items: center;
}

.contacts-btns > li {
    list-style: none;
    padding: 10px;
}

.contacts-reddit {
    font-style: italic;
    font-weight: 500;
    font-size: 14px;
}

.contacts-reddit > a {
    color: inherit;
}

@media(max-width: 767px) {
    body {
        font-size: 16px;
    }

    h1 {
        font-size: 36px;
    }

    h2 {
        font-size: 28px;
    }

    h3 {
        font-size: 18px;
    }

    #mode-toggler {
        font-size: 20px;
        padding: 10px 20px;
    }

    main {
        padding-top: 50px;
    }

    section {
        padding-bottom: 50px;
    }
}
!

JS 

              
                ! function(e, t) {
    "function" == typeof define && define.amd ? define([], t("DarkMode")) : "object" == typeof exports ? module.exports = t("DarkMode") : e.DarkMode = t("DarkMode")
}(this, function(e) {
    "use strict";
    var t = {
        light: !1,
        dark: !1,
        startAt: "21:00",
        endAt: "06:00",
        checkSystemScheme: !0,
        saveOnToggle: !0
    }, o = function(e, o) {
        var r, i = {};
        for (r in t) Object.prototype.hasOwnProperty.call(t, r) && (i[r] = t[r]);
        for (r in o) Object.prototype.hasOwnProperty.call(o, r) && (i[r] = o[r]);
        return i
    }, r = document.getElementsByTagName("head")[0],
        i = document.getElementsByTagName("body")[0],
        n = function(e) {
            var t = new Date,
                o = e.split(":");
            return t.setHours(o[0], o[1], 0, 0)
        }, s = function(e) {
            return "light" === e ? "dark" : "light"
        };

    function d(e) {
        this.options = o(t, e), this.init()
    }
    return d.prototype = {
        init: function() {
            this.options.saveOnToggle || localStorage.removeItem("dm-mode");
            var e = this.getMode();
            if (this.options.checkSystemScheme && window.matchMedia) {
                var t = this;
                window.matchMedia("(prefers-color-scheme: dark)").addListener(function(e) {
                    return e.matches && t.setMode("dark")
                }), window.matchMedia("(prefers-color-scheme: light)").addListener(function(e) {
                    return e.matches && t.setMode("light")
                })
            }
            return this.setMode(e), !0
        },
        getMode: function() {
            if (this.mode) return this.mode;
            var e = localStorage.getItem("dm-mode");
            if (e) return e;
            if (this.options.checkSystemScheme) {
                var t = this.getSystemScheme();
                if ("auto" !== t) return this.mode = t, this.mode
            }
            var o = n(this.options.startAt),
                r = n(this.options.endAt),
                i = (new Date).getTime();
            return r < i && i > o ? "dark" : "light"
        },
        setMode: function(e) {
            if ("light" !== e && "dark" !== e) return console.error("setMode", "Invalid value"), !1;
            this.mode = e;
            var t, o, n, d = s(e);
            if (this.options[e]) {
                var a = document.getElementById("dm-" + e),
                    m = document.getElementById("dm-" + d);
                a ? a && a.removeAttribute("disabled") : (t = "dm-" + e, o = this.options[e], (n = document.createElement("link")).id = t, n.rel = "stylesheet", n.type = "text/css", n.href = o, r.getElementsByTagName("link")[0] ? r.insertBefore(n, r.getElementsByTagName("link")[0]) : r.appendChild(n)), m && m.setAttribute("disabled", !0)
            }
            return i.classList.add("dm-" + e), i.classList.remove("dm-" + d), !0
        },
        isModeSaved: function() {
            return Boolean(localStorage.getItem("dm-mode"))
        },
        clearSavedMode: function() {
            return localStorage.removeItem("dm-mode"), !0
        },
        toggleMode: function() {
            var e = s(this.mode);
            return this.setMode(e), this.options.saveOnToggle && localStorage.setItem("dm-mode", e), e
        },
        toggleTheme: function() {
            return this.toggleMode()
        },
        getSystemScheme: function() {
            if (window.matchMedia) {
                if (window.matchMedia("(prefers-color-scheme: dark)").matches) return "dark";
                if (window.matchMedia("(prefers-color-scheme: light)").matches) return "light"
            }
            return "auto"
        }
    }, d
});

		var DarkMode = new DarkMode({
			light: 'https://nickdeny.github.io/darkmode-js/light.css',
			dark: 'https://nickdeny.github.io/darkmode-js/dark.css',
    })
    
    var ModeToggler = document.getElementById('mode-toggler')
    changeTogglerText()

	  ModeToggler.onclick = function() {
      DarkMode.toggleMode()
      changeTogglerText()
    }
    
    function changeTogglerText() {
      var currentMode = DarkMode.getMode()
      ModeToggler.textContent = currentMode === 'light'  ? 'To dark 🌝' : 'To light 🌚'
    }
!
999px

Console