Recreating Codepen

Recreating Codepen by Wes Bos

HTML

<link rel="stylesheet" href="https://cdn.rawgit.com/wesbos/css-grid/master/assets/style.css">
<div class="codepen">
  <header class="pen">
    <div class="pen__details">
      <h1>Some Amazing Pen Name</h1>
      <p class="pen__author">A Pen by Wes Bos</p>
    </div>
    <button class="button button--dirty">☁️ Save</button>
    <button class="button">️️☁️ Save As Private</button>
    <button class="button">⚙ Settings</button>
    <button class="button">👀 Change View</button>
    <img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/28831/profile/profile-80.jpg?1" alt="Wes Bos" height="44">
  </header>
  <section class="code">
    <div class="editor">
      <header class="editor__header">
        <button class="button button--small editor__settings">⚙</button>
        <h3 class="editor__heading">HTML</h3>
        <button class="button button--small editor__settings">⌄</button>
      </header>
      <div class="editor__code">
        <div class="editor__gutter">
          <span class="editor__number">1</span>
        </div>

        <textarea class="editor__input"><p>Oh Hey There!</p></textarea>
      </div>
    </div>
    <div class="editor">
      <header class="editor__header">
        <button class="button button--small editor__settings">⚙</button>
        <h3 class="editor__heading">CSS</h3>
        <button class="button button--small editor__settings">⌄</button>
      </header>
      <div class="editor__code">
        <div class="editor__gutter">
          <span class="editor__number">1</span>
          <span class="editor__number">2</span>
          <span class="editor__number">3</span>
        </div>

        <textarea class="editor__input">.codepen {
is: cool;
}
        </textarea>
      </div>

    </div>
    <div class="editor">
      <header class="editor__header">
        <button class="button button--small editor__settings">⚙</button>
        <h3 class="editor__heading">JS</h3>
        <button class="button button--small editor__settings">⌄</button>
...

CSS

:root {
  --grey: #343436;
}
html {
  box-sizing: border-box;
  font-family: "Lato", "Lucida Grande", "Lucida Sans Unicode", Tahoma,
    Sans-Serif;
  font-weight: normal;
  color: #272727;
  text-shadow: 0 2px 0 rgba(0, 0, 0, 0.07);
}

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

body {
  margin: 0;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  font-weight: normal;
  margin: 0;
  font-size: 1.5em;
}

.codepen {
  display: grid;
  grid-template-rows: auto 1fr 1fr auto;
  height: 100vh;
  color: white;
}

.codepen >* {
  border:1px solid black;
}


/* Editor! */
.code {
  display:grid;
  grid-template-columns: repeat(3, 1fr);
  background: #1b2b34;
}

.editor {
  display: grid;
  grid-template-rows: auto 1fr;
}

.editor__header {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  padding: 5px;
  grid-gap: 5px;
  background: rgba(0,0,0,0.1);
}

.editor__code {
  display: grid;
  grid-template-columns: auto 1fr;
}

.editor__number {
  display: block;
  padding: 0 10px;
}

.editor__input {
  resize: none;
  background: none;
  border: 0;
  color: grey;
  font-size: 16px;
  line-height: 19px;
}

/* Pen Header */

.pen {
  display: grid;
  grid-template-columns: 1fr;
  grid-auto-flow: column;
  align-items: center;
  grid-gap: 10px;
  background: black;
  border-bottom: 5px solid var(--grey);
  color: white;
  padding: 10px;
}

.preview {
  display: grid;
}

/* Buttons */

.button {
  background: var(--grey);
  border: 0;
  color: white;
  padding: 10px;
  border-radius:5px;
  font-size: 15px;
  position: relative;
}

.button--small {
  font-size: 12px;
  padding: 4px;
}

.button--dirty:before {
  background: #ffc600;
  display: block;
  content: '';
  height: 2px;
  width: calc(100% - 6px);
  position: absolute;
  left: 3px;
  top: 3px;
}


.settings {
  padding: 5px;
  background: black;
  border-top: 1px solid grey;
}