css Audio - Active file-generic CSS - Active Generic - Active HTML - Active JS - Active SVG - Active Text - Active file-generic Video - Active header Love html icon-new-collection icon-person icon-team numbered-list123 pop-out spinner split-screen star tv

Pen Settings

CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

+ add another resource

You're using npm packages, so we've auto-selected Babel for you here, which we require to process imports and make it all work. If you need to use a different JavaScript preprocessor, remove the packages in the npm tab.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

+ add another resource

Use npm Packages

We can make npm packages available for you to use in your JavaScript. We use webpack to prepare them and make them available to import. We'll also process your JavaScript with Babel.

⚠️ This feature can only be used by logged in users.

Code Indentation


Save Automatically?

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

              <div class="page-wrap">
  <header class="container">
    <h1 class="title-project"><a href="https://atelierbram.github.io/lazy-loading-logos/" class="title-project_link"><span class="screen-reader-text">Lazy Loading Logos</span><img data-src="https://atelierbram.github.io/lazy-loading-logos/assets/img/svg/logo-lll_456x60.svg" src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='456' height='60' viewBox='0 0 456 60'%3E%3Ctext x='16' y='43' style='text-anchor:start;font-size:44px;font-family:Calibri,AvenirNextCondensed-DemiBold,Segoe UI,Tahoma,sans-serif;font-weight:bold;letter-spacing:-.4px;fill:rgb(34,34,34)'%3ELazy Loading Logos%3C/text%3E%3C/svg%3E" alt="logo for Lazy Loading Logos" class="logo" width="456" height="60"></a></h1>

  <main class="container">
      <p>Reload the page and see the header image replacement in action.</p>
      <p>Read about more about it <a href="https://codepen.io/atelierbram/post/lazy-loading">in this blogpost</a></p>
      <p class="note">There is an added delay in the javascript function used on this page: this is only for this demo, so not for production use. Use the script at: <code><a href="//atelierbram.github.io/lazy-loading-logos/assets/js/load-img.js">atelierbram.github.io/lazy-loading-logos/assets/js/load-img.js</a></code></p>


  <footer class="site-footer">
    <small class="colophon">Made by <a href="http://atelierbramdehaan.nl/">Atelier Bram de Haan</a>, on <a href="https://github.com/atelierbram/lazy-loading-logos/">GitHub</a>.</small>
  </footer><a href="https://github.com/atelierbram/lazy-loading-logos/" class="github-corner"><svg width="72" height="72" viewBox="0 0 250 250" style="fill:#2a2734;position:absolute;top:0;border:0;right:0;"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg></a>
              img {
  max-width: 100%;
  height: auto;

.title-project {
  width: 456px;

.title-project_link {
  display: block;
  position: relative;
  height: 0;
  padding-bottom: 13.15789473684211%;

.logo {
  position: absolute;
  width: 100%;
  height: 100%;

.screen-reader-text {
  border: 0;
  clip: rect(0 0 0 0);
  height: 1px;
  margin: -1px;
  overflow: hidden;
  padding: 0;
  position: absolute;
  width: 1px;
  white-space: nowrap;

// general
*::after {
  margin: 0;
  padding: 0;
  box-sizing: inherit;
  // outline: 1px dotted salmon;

body {
  height: 100%;
  background-color: hsl(144, 43%, 66%);

body {
  font: 100%/1.5 -apple-system, BlinkMacSystemFont, Calibri, "Segoe UI", AvenirNext-Regular, Verdana, sans-serif;
  box-sizing: border-box;

.page-wrap {
  position: relative;
  padding-bottom: 60px;
  min-height: 100vh;
  background-image: linear-gradient(to bottom, #f0f0f0, #f0f0f0 72px, transparent 0, transparent),url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='1000' height='100' viewBox='0 0 1000 100'%3E%3Crect fill='rgb(255,255,255)' width='1200' height='100'/%3E%3C/svg%3E");
  background-repeat: no-repeat, repeat-y;
  background-position: 0 0, center;

.container {
  max-width: 56em;
  margin: 0 auto;

header {
  padding-top: 4px;

main > article {
  padding: 3em 1em;

  @media (min-width: 800px) {
    padding-left: 3em;
    padding-right: 3em;

main > article p {
  max-width: 35em;

main > article p:first-of-type {
  position: relative;

main > article p:first-of-type:after {
  content: "\021EA \00A0 \021EA \00A0 \021EA";
  position: absolute;
  text-align: center;
  font-size: 3em;

.site-footer {
  position: absolute;
  height: 60px;
  text-align: center;
  background-color: #f0f0f0;

.colophon {
  display: inline-block;
  padding-top: 1.5em;

.github-corner {
  visibility: hidden;
  color: #f0f0f0;

  @media (min-width: 517px) {
    visibility: visible;

.github-corner:hover {
  color: hsl(144, 43%, 66%);

a {
  color: hsl(236, 75%, 45%);

h3 {
  text-transform: uppercase;
  color: #222;
  font-size: 1.25em;
  margin-top: 1em;

p {
  padding: .5em 0;

.note {
  margin: 2em 0 3em;
  padding: 1em 1.5em;
  background-color: hsl(54,77%,83%);
  border-radius: 3px;

// IE11 still needs this:
footer {
  display: block;
 * http://blog.simonwillison.net/post/57956760515/addloadevent
 * http://www.sitepoint.com/closures-and-executing-javascript-on-page-load/
function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {

function loadImg(){
  var imgDefer = document.querySelectorAll('[data-src]')

    // Timeout function is only for demo purpose: it adds an delay of half a second
    setTimeout(function() { // this line can be removed, see: https://github.com/atelierbram/lazy-loading-logos/blob/master/docs/assets/js/load-img.js

    for (var i=0; i<imgDefer.length; i++) {
      if(imgDefer[i].getAttribute('data-src')) {


  }, 500); // this line can be removed, see: load-img.js

🕑 One or more of the npm packages you are using needs to be built. You're the first person to ever need it! We're building it right now and your preview will start updating again when it's ready.
Loading ..................