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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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HTML 

              
                <header class="header" role="banner">
    <h1 class="page-title">
      <a href="#">
        <img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/182774/knowledge-space.svg" alt="">
        <span><strong>Knowledge</strong> Space</span>
      </a>
    </h1>
  </header>

  <article class="hero">
    <div class="container hero__wrapper">
      <ul class="tags">
        <li class="tags__item"><a href="#">web design</a></li>
        <li class="tags__item"><a href="#">frontend</a></li>
        <li class="tags__item"><a href="#">css</a></li>
      </ul>
      <h2 class="hero__title">Comprehensive Guide to Build Dynamic and Resizable Components in CSS</h2>
      <div class="bio">
        <img class="bio__avatar" src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/182774/shadeed.jpg" alt="">
        <div class="bio__meta">
          By: <strong>Ahmad Shadeed</strong>
          <time>Published on August 5, 2016</time>
        </div>
      </div>
    </div>
  </article>

  <div class="container">
    <div class="layout">
      <main class="layout__item layout__item--primary" role="main">
        <section class="section">
          <h2 class="section__title">
            <span>Course Outline</span>
          </h2>

          <div class="section__content">
            <ul class="list">
              <li class="list__item">
                <span>What is the difference between EM, REM and PX units?</span>
                <ul>
                  <li class="list__subitem">Sub point example</li>
                  <li class="list__subitem">Sub point example</li>
                  <li class="list__subitem">Sub point example</li>
                </ul>
              </li>
              <li class="list__item">How we can get benefit from using EM and REM?</li>
              <li class="list__item">Different examples and use cases for EM based components.</li>
            </ul>
          </div>
        </section>

        <section class="section">
          <h2 class="section__title">
            <span>Course Registeration</span>
          </h2>

          <div class="section__content">
            <form class="form" action="">
              <p class="form__item">
                <label for="name">Full Name:</label>
                <input type="text" id="name" aria-required="true" required placeholder="John Smith">
              </p>
              <p class="form__item">
                <label for="email">Email Address:</label>
                <input type="email" id="email" aria-required="true" required placeholder="mail@example.com">
              </p>
              <p>
                <button class="button">Register</button>
              </p>
            </form>
          </div>
        </section>

        <section class="section">
          <h2 class="section__title">
            <span>Student Feedback</span>
          </h2>

          <div class="section__content">
            <blockquote class="quote">
              <p>One of the best courses I’ve ever watched. Highly recommended and you will be happy by the result. The instructor
                teaches in a way that is very easy and awesome. - John Smith</p>
            </blockquote>
          </div>
        </section>
      </main>
      <aside class="layout__item layout__item--aside" role="complementary">
        <section class="section">
          <h2 class="section__title section__title--sub"><span>Featured Students</span></h2>

          <div class="section__content">
            <ul>
              <li>
                <a href="#">
                  <div class="bio">
                    <img class="bio__avatar" src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/182774/shadeed.jpg" alt="">
                    <div class="bio__meta">
                      Ahmad Shadeed
                      <span>32 points</span>
                    </div>
                  </div>
                </a>
              </li>
              <li>
                <a href="#">
                  <div class="bio">
                    <img class="bio__avatar" src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/182774/shadeed.jpg" alt="">
                    <div class="bio__meta">
                      Ahmad Shadeed
                      <span>32 points</span>
                    </div>
                  </div>
                </a>
              </li>
              <li>
                <a href="#">
                  <div class="bio">
                    <img class="bio__avatar" src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/182774/shadeed.jpg" alt="">
                    <div class="bio__meta">
                      Ahmad Shadeed
                      <span>32 points</span>
                    </div>
                  </div>
                </a>
              </li>
            </ul>
          </div>
        </section>
      </aside>
    </div>
  </div>
<footer role="contentinfo">
<div>Demo logo made by <a href="http://www.flaticon.com/authors/zlatko-najdenovski" title="Zlatko Najdenovski">Zlatko Najdenovski</a> from <a href="http://www.flaticon.com" title="Flaticon">www.flaticon.com</a> is licensed by <a href="http://creativecommons.org/licenses/by/3.0/" title="Creative Commons BY 3.0" target="_blank">CC 3.0 BY</a></div>
</footer>
!

CSS 

              
                .visually-hidden {
  position: absolute;
  height: 1px;
  width: 1px;
  overflow: hidden;
  clip: rect(1px, 1px, 1px, 1px); }

html,
body,
div,
span,
h1,
h2,
h3,
h4,
h5,
h6,
p,
blockquote,
a,
abbr,
img,
small,
strong,
ol,
ul,
li,
form,
label,
article,
aside,
footer,
header {
  margin: 0;
  padding: 0;
  border: 0;
  font-size: 100%;
  font: inherit;
  vertical-align: baseline; }

ol,
ul,
li {
  list-style: none; }

li {
  margin-bottom: 1em; }

html {
  box-sizing: border-box; }

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

a {
  text-decoration: none;
  color: inherit; }

button,
input,
textarea {
  color: inherit;
  font-style: inherit;
  font-weight: inherit; }

strong {
  font-weight: 700; }

input {
  appearance: none; }

body {
  font-family: 'Source Sans Pro', sans-serif; }

body {
  background: #fff;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale; }

.container {
  position: relative;
  max-width: 73.125em;
  padding-left: 1em;
  padding-right: 1em;
  margin-left: auto;
  margin-right: auto; }
  .container:after {
    content: '';
    display: block;
    clear: both; }

@media (min-width: 75em) {
  .container {
    padding-left: 0;
    padding-right: 0; } }
.header {
  background: #5066C2;
  text-align: center; }

/*------------------------------------*\
    footer
\*------------------------------------*/
.section {
  padding-top: 1em;
  padding-bottom: 1em; }

.section__title {
  border-bottom: 1px solid #d4d4d4;
  font-size: 1.25em;
  color: #5066C2;
  font-weight: 700;
  margin-bottom: 0.85em; }
  .section__title span {
    display: inline-block;
    background: linear-gradient(#5066C2, #5066C2) repeat-x;
    background-size: 100% 3px;
    background-position: bottom center;
    padding: 0.5em 0.875em; }
  .section__title--sub {
    color: #4a4a4a;
    border-bottom: 0; }
    .section__title--sub span {
      background-size: 0; }

@media (min-width: 55em) {
  .section__content {
    padding-right: 2em; } }
.layout__item--aside .section__content {
  padding-left: 1em;
  padding-right: 1em; }

.form__item {
  margin-bottom: 1em; }
  .form__item label {
    display: block;
    margin-bottom: 0.35em; }
  .form__item input {
    border: 2px solid #B4B4B4;
    padding: 0.75em 0.5em;
    font-size: 16px;
    border-radius: 0.25em;
    width: 100%;
    max-width: 25em; }
    .form__item input:focus {
      outline: 0;
      border-color: #5066C2;
      box-shadow: 0 0 0.3125em 0.125em rgba(80, 102, 194, 0.5); }

@media (min-width: 55em) {
  .layout__item {
    float: left; } }

.layout__item--aside {
  background: #fbfbfb;
  border-left: 1px solid #d9D9d9;
  border-right: 1px solid #d9D9d9; }

@media (min-width: 55em) {
  .layout {
    display: flex; }

  .layout__item--primary {
    width: 70%; }

  .layout__item--aside {
    width: 30%; } }
.page-title {
  font-size: 1.15rem;
  color: #fff; }
  .page-title a {
    display: inline-block;
    border-bottom: 0.25em solid rgba(0, 0, 0, 0.15);
    padding-bottom: 0.25em;
    padding-top: 0.35em; }
  .page-title img {
    display: inline-block;
    vertical-align: middle;
    width: 2.1875em;
    height: 2.375em; }
  @media (min-width: 55em) {
    .page-title {
      font-size: 1.5rem; } }

.hero {
  background: #f4f4f4;
  border-bottom: 1px solid #d9d9d9;
  padding-top: 2em;
  padding-bottom: 2em; }

.hero__wrapper > *:not(:last-child) {
  margin-bottom: 0.7rem; }

/* I need to find a workaround for using large font sizes with things to be based */
/* on 16 px font size */
.hero__title {
  font-size: 1.5em;
  font-weight: bold;
  color: #5066C2;
  max-width: 20em; }
  @media (min-width: 55em) {
    .hero__title {
      font-size: 2.5em; } }

.tags__item {
  display: inline-block;
  font-size: 0.875em; }
  .tags__item a {
    display: block;
    padding: 0.25em 0.75em;
    background: #d4d4d4;
    border-radius: 20px;
    min-width: 60px;
    text-align: center; }
    .tags__item a:hover {
      background: #5066C2;
      color: #fff; }

.bio {
  display: flex;
  font-size: 1em; }
  @media (min-width: 55em) {
    .bio {
      font-size: 1.125em; } }

.bio__avatar {
  width: 2.75em;
  height: 2.75em;
  border-radius: 50%;
  margin-right: 0.5em;
  object-fit: cover;
}

.bio__meta {
  color: #4a4a4a; }
  .bio__meta time,
  .bio__meta span {
    display: block;
    font-size: 85%;
    margin-top: 0.25em; }

.list {
  counter-reset: list; }

.list__item {
  font-size: 1em;
  margin-bottom: 0.8em; }
  .list__item:before {
    content: counter(list);
    counter-increment: list; }
  .list__item ul {
    counter-reset: sublist;
    font-size: 1em; }

.list__subitem {
  padding-left: 1.5em;
  font-size: 90%; }
  .list__subitem:not(:last-child) {
    margin-bottom: 0.7em; }
  .list__subitem:before {
    content: counter(list) "." counter(sublist);
    counter-increment: sublist; }
  .list__subitem span {
    font-size: 1em; }

.list__item,
.list__subitem {
  position: relative;
  min-height: 2.5em;
  padding-left: 2.75em;
  line-height: 2.5em; }
  .list__item:before,
  .list__subitem:before {
    position: absolute;
    left: 0;
    display: inline-block;
    width: 2.5em;
    height: 2.5em;
    background: lightgrey;
    border-radius: 50%;
    text-align: center;
    line-height: 2.5em;
    margin-right: 0.5rem; }

.button {
  background: #5066C2;
  border-radius: 0.25em;
  padding: 0.75em 1.25em;
  color: #fff;
  border: 0;
  font-size: 1em; }

.quote {
  position: relative;
  background: #ebebeb;
  padding: 1em;
  padding-left: 4.375em;
  border: 0.125em solid #bcbcbc;
  border-radius: 0.25em; }
  .quote:before {
    content: "";
    position: absolute;
    left: 1.375em;
    top: 1.5em;
    background: url("https://s3-us-west-2.amazonaws.com/s.cdpn.io/182774/quotes1.svg") no-repeat;
    background-size: 100%;
    width: 2.25em;
    height: 1.5625em; }
  .quote p {
    font-size: 1.5em; }

footer {
  padding: 1em;
  border-top: 1px solid grey;
  text-align: center;
}

footer a {
  color: #5066C2;
  text-decoration: underline;
}

footer a:hover {
  opacity: 0.8;
}
!

JS
!
999px

Console