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CSS

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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

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Vendor Prefixing

About Vendor Prefixing

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HTML 

              
                <ol id="slides">
  <li class="slide slide--text">
    <div class="content">
      <h1>The Modern CSS Toolkit</h1>
      <p>Presented by Stephanie Eckles</p>
      <p><a target="_blank" href="https://twitter.com/5t3ph">@5t3ph</a> • <a target="_blank" href="https://moderncss.dev">ModernCSS.dev</a> • <a target="_blank" href="https://smolcss.dev">SmolCSS.dev</a></p>
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h2>🤔 What is "Modern CSS"?</h2>
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h3>🤩⚡️💡 TL;DR:</h3>
      <p>All the stuff that eliminates the hacks we used to need</p>
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h2>Toolkit Contents</h2>
      <ul>
        <li>Layout Techniques</li>
        <li>New and Enhanced Selectors</li>
        <li>Super-Charged Properties</li>
      </ul>
    </div>
  </li>
  <li class="slide slide--title" data-topic="Layout">
    <div class="content">
      <h2>🔨 Layout Techniques</h2>
    </div>
  </li>
<!--  modern container -->
  <li class="slide slide--demo" data-topic="Layout">
<div class="style">
<style contenteditable="true" style="--num-lines: 5">
.modern-container {
  --container-width: 40ch;

  width: min(
    var(--container-width), 100% - 3rem
  );
  margin-inline: auto;
}
</style>
</div>
  <div class="demo container">
    <div class="modern-container">
      <div class="box">container</div>
    </div>
  </div>
</li>
<!--  centering -->
  <li class="slide slide--demo" data-topic="Layout">
    <div class="style">
      <style contenteditable="true" style="--num-lines: 2">
.centering {
  display: grid;
  place-content: center;
}
      </style>
    </div>

    <div class="container centering">
      <div class="box">centering</div>
    </div>
  </li>
<!--  grid -->
  <li class="slide slide--demo" data-topic="Layout">
    <div class="style">
      <style contenteditable="true" style="--highlight-start: calc(5 * var(--line-height));  --num-lines: 2">
.grid {
  display: grid;
  /* grid-template-columns: 
    repeat(3, 1fr); */
  grid-template-columns: 
    repeat(auto-fit, minmax(15ch, 1fr));
}
      </style>
    </div>

    <div class="container demo grid">
      <div class="box centering">a</div>
      <div class="box centering">b</div>
      <div class="box centering">c</div>
      <div class="box centering">d</div>
      <div class="box centering">e</div>
    </div>
  </li>
<!--  fit-content -->
  <li class="slide slide--demo" data-topic="Layout">
    <div class="style">
      <style contenteditable="true">
.fit-content {
  width: fit-content;
}
      </style>
    </div>

    <div class="container demo">
      <p class="fit-content" contenteditable spellcheck="false">Edit me!</p>
    </div>
  </li>
<!--  grid fit-content -->
  <li class="slide slide--demo" data-topic="Layout">
    <div class="style">
      <style contenteditable="true" style="--highlight-start: calc(3 * var(--line-height)); --num-lines: 2">
.grid-fit-content {
  display: grid;
  grid-template-columns: 
    fit-content(15ch) 1fr;
}
      </style>
    </div>

    <div class="demo centering">
      <div class="grid-fit-content container">
        <div contenteditable spellcheck="false">Ipsum</div>
        <div>Lorem ipsum dolor sit amet.</div>
      </div>
    </div>
  </li>
  <li class="slide slide--title" data-category="Selectors">
    <div class="content">
      <h2>🔧 New and Enhanced Selectors</h2>
    </div>
  </li>
<!--  :is -->
  <li class="slide slide--demo" data-topic="Selectors">
    <div class="style">
      <style contenteditable="true" class="highlight--rule-only">
/* Try changing to :where() */
:is(#id, h1, h2, h3) {
  margin-bottom: 0.65em;
}
        
h2 {
  margin-bottom: 2rem;
}
      </style>
    </div>

    <div class="modern-container centering demo">
        <h1>Headline 1</h1>
        <h2>Headline 2</h2>
        <h3>Headline 3</h3>
    </div>
  </li>
<!--  :not -->
  <li class="slide slide--demo" data-topic="Selectors">
    <div class="style">
      <style contenteditable="true" class="highlight--rule-only"> 
a:not([class], nav *) {
  color: mediumvioletred;
}
      </style>
    </div>

    <div class="modern-container centering demo" style="--gap: 2rem;">
      <nav><a href="#">nav link</a></nav>
      <p><a href="#">content link</a></p>
      <a href="#" class="button">.button link</a>
    </div>
  </li>
<!--  :focus-visible -->
  <li class="slide slide--demo" data-topic="Selectors">
    <div class="style">
      <style contenteditable="true" class="highlight--rule-only">
button:focus-visible {
  outline: 2px solid currentColor;
  outline-offset: 2px;
}
        
button:focus {
  outline: 2px solid currentColor;
  outline-offset: 2px;
}
        
button:focus:not(:focus-visible) {
  outline: none;
}
      </style>
    </div>

    <div class="modern-container centering demo" style="--gap: 2rem;">
      <button type="button">Button 1</button>
      <button type="button">Button 2</button>
    </div>
  </li>
<!--  :focus-within -->
  <li class="slide slide--demo" data-topic="Selectors">
    <div class="style">
      <style contenteditable="true" class="highlight--rule-only"> 
.fw-demo:focus-within {
  outline: 2px dashed currentColor;
  outline-offset: -1rem;
}
      </style>
    </div>

    <div class="fw-demo modern-container centering demo" style="--gap: 2rem;">
      <button type="button">Button 1</button>
      <button type="button">Button 2</button>
    </div>
  </li>
<!--  ::marker -->
  <li class="slide slide--demo" data-topic="Selectors">
    <div class="style">
      <style contenteditable="true" class="highlight--rule-only"> 
::marker {
  color: mediumvioletred;
  font-size: 1.25em;
}
      </style>
    </div>

    <div class="modern-container centering demo">
      <ul>
        <li>Item 1</li>
        <li>Item 2</li>
        <li>Item 3</li>
      </ul>
    </div>
  </li>
  <li class="slide slide--title" data-category="Properties">
    <div class="content">
      <h2>⚙️ Super-Charged Properties</h2>
    </div>
  </li>
<!--  aspect-ratio -->
  <li class="slide slide--demo" data-topic="Properties">
    <div class="style">
      <style contenteditable="true"  style="--num-lines: 2">
.aspect-ratio {
  /* Try options like 1 or 3/2 */
  aspect-ratio: ?;
}
      </style>
    </div>

    <div class="container centering demo">
      <div class="aspect-ratio centering">aspect-ratio</div>
    </div>
</li>
<!--  object-fit -->
  <li class="slide slide--demo" data-topic="Properties">
    <div class="style">
      <style contenteditable="true" style="--highlight-start: calc(3 * var(--line-height))">       
img.object-fit {
  aspect-ratio: 1;
  object-fit: cover;
  object-position: right;
  width: 100%;
}
      </style>
    </div>

    <div class="container modern-container centering demo" style="--container-width: 30ch;">
        <img src="https://source.unsplash.com/vYpbBtkDhNE/1600x900" alt="" class="object-fit">
    </div>
  </li>
<!--  accent-color -->
  <li class="slide slide--demo" data-topic="Properties">
    <div class="style">
      <style contenteditable="true"  style="--num-lines: 2"> 
:root {
  /* Try your own color */
  accent-color: ?;
}
      </style>
    </div>

    <div class="modern-container centering demo" style="--gap: 2rem;">
      <label>
        <input type="radio" checked>
        Radio
      </label>
      <label>
        <input type="checkbox" checked>
        Checkbox
      </label>
      <label>
        Range<br>
        <input type="range" min="0" max="100" value="30">
      </label>
      <label>
        Progress<br>
        <progress max="100" value="70">70%</progress>
      </label>
      <p class="note">To fully control form input styling, review the posts on ModernCSS.dev</p>
    </div>
  </li>
<!--  scroll-margin-top -->
  <li class="slide slide--demo" data-topic="Properties">
    <div class="style">
      <style contenteditable="true"  style="--highlight-start: calc(5 * var(--line-height));  --num-lines: 3"> 
[id] {
  /* Try a value like 2rem,
  then click the anchor link */
  scroll-margin-top: ?;
}
</style>
    </div>

    <div class="demo-overflow">
      <div class="modern-container centering demo">
        <p><a href="#anchor">Anchor link</a></p>
        <p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Animi, ratione! Accusamus soluta necessitatibus sunt, molestias cumque magni. Vero dicta officia modi vel explicabo, dolores, deleniti ad facilis a accusamus doloremque?</p>
        <p>Voluptate iusto reprehenderit cupiditate facilis blanditiis vero tempora quasi, rerum impedit odit dignissimos maxime quis ab temporibus maiores repellendus ipsum atque tempore labore est. Sequi repellat earum officia illum hic.</p>
        <p>Earum tempore accusantium quis distinctio illum autem reiciendis quod. At doloremque, quidem accusamus sed odit hic maxime animi? Amet deserunt, ea quis earum velit voluptatum nihil esse vel repellat neque.</p>
        <h2 id="anchor">Anchor heading</h2>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Inventore repellat dolores assumenda odio quis impedit blanditiis officiis, incidunt, accusantium ab nostrum, delectus ea deserunt beatae maxime quia sit voluptatibus enim?</p>
        <p>Unde, ducimus eius. Nobis dolore magnam ipsam sapiente qui reiciendis harum corrupti perspiciatis architecto iste dicta quia fugiat veritatis nisi laudantium quae aspernatur omnis error incidunt, facere sunt molestiae blanditiis.</p>
        <p>Aliquam modi perferendis dignissimos ut qui amet perspiciatis ipsum omnis ex, quam maxime illo minima incidunt sint ducimus dolorum quisquam similique quae maiores iste eos molestiae. Aliquam labore repellendus eveniet.</p>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Blanditiis veniam esse non, id ducimus excepturi repellendus ab eos ut laudantium quae nulla cumque quos voluptatum quibusdam repudiandae, aut molestias amet.</p>
        <p>Voluptatum, cupiditate aut hic eos iure expedita saepe molestiae quo vero sit nihil deserunt? Vel ullam nostrum nobis, aperiam quos reiciendis, magnam itaque facere saepe atque provident laudantium eveniet exercitationem!</p>
        <p>Voluptates delectus obcaecati totam reiciendis cupiditate ab nesciunt sint, blanditiis corrupti laboriosam tenetur dolor rerum aliquam repellat reprehenderit sunt earum laborum fuga recusandae minus porro modi. Cum soluta ea repellat?</p>
      </div>
    </div>
  </li>
<!--  scroll-margin-bottom -->
  <li class="slide slide--demo" data-topic="Properties">
    <div class="style">
      <style contenteditable="true" style="--num-lines: 3"> 
a {
  /* Try a value like 8vh then
  tab between the links in the content */
  scroll-margin-bottom: ?;
}
</style>
    </div>

    <div class="demo-overflow">
      <div class="modern-container centering demo">
        <p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Animi, ratione! Accusamus soluta necessitatibus sunt, molestias cumque magni. Vero dicta officia modi vel explicabo, dolores, deleniti ad facilis a accusamus doloremque?</p>
        <p>Voluptate iusto reprehenderit cupiditate facilis blanditiis vero tempora quasi, rerum impedit odit dignissimos maxime quis ab temporibus maiores repellendus ipsum atque tempore labore est. Sequi repellat earum officia illum hic.</p>
        <p>Earum tempore accusantium quis distinctio illum autem reiciendis quod. At doloremque, quidem accusamus sed odit hic maxime animi? Amet deserunt, ea quis earum velit voluptatum nihil esse vel repellat neque.</p>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Inventore repellat dolores assumenda odio quis impedit blanditiis officiis, incidunt, accusantium ab nostrum, delectus ea deserunt beatae maxime quia sit voluptatibus enim?</p>
        <p>Unde, <a href="#">ducimus eius</a>. Nobis dolore magnam ipsam sapiente qui reiciendis harum corrupti perspiciatis architecto iste dicta quia fugiat veritatis nisi laudantium quae aspernatur omnis error incidunt, facere sunt molestiae blanditiis.</p>
        <p>Aliquam modi perferendis dignissimos ut qui amet perspiciatis ipsum omnis ex, quam maxime illo minima incidunt sint ducimus dolorum quisquam similique quae maiores iste eos molestiae. <a href="#">Aliquam labore repellendus eveniet</a>.</p>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Blanditiis veniam esse non, id ducimus excepturi repellendus ab eos ut laudantium quae nulla cumque quos voluptatum quibusdam repudiandae, aut molestias amet.</p>
        <p>Voluptatum, cupiditate aut hic eos iure expedita saepe molestiae quo vero sit nihil deserunt? Vel ullam nostrum nobis, aperiam quos reiciendis, magnam itaque facere saepe atque provident laudantium eveniet exercitationem!</p>
        <p>Unde, <a href="#">ducimus eius</a>. Nobis dolore magnam ipsam sapiente qui reiciendis harum corrupti perspiciatis architecto iste dicta quia fugiat veritatis nisi laudantium quae aspernatur omnis error incidunt, facere sunt molestiae blanditiis.</p>
        <p>Aliquam modi perferendis dignissimos ut qui amet perspiciatis ipsum omnis ex, quam maxime illo minima incidunt sint ducimus dolorum quisquam similique quae maiores iste eos molestiae. <a href="#">Aliquam labore repellendus eveniet</a>.</p>
        <p>Voluptates delectus obcaecati totam reiciendis cupiditate ab nesciunt sint, blanditiis corrupti laboriosam tenetur dolor rerum aliquam repellat reprehenderit sunt earum laborum fuga recusandae minus porro modi. Cum soluta ea repellat?</p>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Blanditiis veniam esse non, id ducimus excepturi repellendus ab eos ut laudantium quae nulla cumque quos voluptatum quibusdam repudiandae, aut molestias amet.</p>
        <p>Voluptatum, cupiditate aut hic eos iure expedita saepe molestiae quo vero sit nihil deserunt? Vel ullam nostrum nobis, aperiam quos reiciendis, magnam itaque facere saepe atque provident laudantium eveniet exercitationem!</p>
        <p>Unde, <a href="#">ducimus eius</a>. Nobis dolore magnam ipsam sapiente qui reiciendis harum corrupti perspiciatis architecto iste dicta quia fugiat veritatis nisi laudantium quae aspernatur omnis error incidunt, facere sunt molestiae blanditiis.</p>
        <p>Aliquam modi perferendis dignissimos ut qui amet perspiciatis ipsum omnis ex, quam maxime illo minima incidunt sint ducimus dolorum quisquam similique quae maiores iste eos molestiae. <a href="#">Aliquam labore repellendus eveniet</a>.</p>
        <p>Voluptates delectus obcaecati totam reiciendis cupiditate ab nesciunt sint, blanditiis corrupti laboriosam tenetur dolor rerum aliquam repellat reprehenderit sunt earum laborum fuga recusandae minus porro modi. Cum soluta ea repellat?</p>
      </div>
    </div>
  </li>
<!--  touch media query -->
  <li class="slide slide--demo">
    <div class="style">
      <style contenteditable="true" class="highlight--none"> 
.icons {
  gap: 1rem;
}

.icon {
  width: 44px;
}

@media (any-hover: hover) and (any-pointer: fine) {
  .icons {
    gap: .5rem;
  }

  .icon {
    width: 36px;
  }
}
</style>
    </div>

    <div class="modern-container centering demo">
      <ul class="icons container">
        <li class="icon centering">1</li>
        <li class="icon centering">2</li>
        <li class="icon centering">3</li>
      </ul>
    </div>
  </li>
<!--  @supports -->
  <li class="slide slide--style-only">
    <div class="style" >
      <style contenteditable="true" style="--highlight-start: calc(5 * var(--line-height))">
.supports-aspect-ratio {
  aspect-ratio: 1;
}

@supports not (aspect-ratio: 1) {
  .supports-aspect-ratio {
    max-height: 25vh;
  }
}
      </style>
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h2>webhint VS Code extension</h2>
      <p>Check support during development</p>
      <p>Support calculated based on your <code>browserslist</code></p>
      
      <img src="https://assets.codepen.io/1101822/Screen+Shot+2021-11-28+at+2.22.17+PM.png" alt="Preview of webhint popover in VS Code, with text: 'accent-color' is not supported by Chrome < 93, Edge < 93, Firefox < 92, Opera < 79, Safari, Safari on iOS, Samsung Internet. webhint (compat-api/css)" />
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h2>Upcoming Toolkit Additions</h2>
      <ul>
        <li>Container queries</li>
        <li>Layers</li>
        <li>Scope</li>
        <li>Color functions</li>
        <li>:has()</li>
        <li>...<em>so much more</em></li>
      </ul>
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h2>.slide:last-of-type</h2>
      <p>These slides were built with zero JS thanks to <strong>CSS Scroll Snap</strong></p>
      <p>🤓 Plus the HTML attribute <code>contenteditable</code> used within Firefox allowed the exposed <code>&lt;style&gt;</code> to be fully editable</p>
      <p>💜 And the wonderfulness of the CSS cascade compounding each demo's styles to enable other slide styles</p>
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h1>Modern CSS Challenges</h1>
      <p>Guided practice to level-up your CSS skills</p>
      <p><a target="_blank" href="https:/challenges.moderncss.dev">challenges.moderncss.dev</a></p>
    </div>
  </li>
  <li class="slide slide--text">
    <div class="content">
      <h1>The Modern CSS Toolkit</h1>
      <p>Presented by Stephanie Eckles</p>
      <p><a target="_blank" href="https://twitter.com/5t3ph">@5t3ph</a> • <a target="_blank" href="https://moderncss.dev">ModernCSS.dev</a> • <a target="_blank" href="https://smolcss.dev">SmolCSS.dev</a></p>
    </div>
  </li>
</ol>
!

CSS 

              
                :root {
  --theme-hue: 260;
  --theme-saturation: 85%;
  --theme-hs: var(--theme-hue), var(--theme-saturation);
}

* {
  margin: 0;
  box-sizing: border-box;
}

body {
  padding: 0;
  min-height: 100vh;
  font-family: system-ui, sans-serif;
  font-size: 1.5rem;
  background-color: hsl(var(--theme-hs), 95%);
  color: hsl(var(--theme-hs), 25%);
}

body,
#slides,
.slide {
  display: grid;
}

#slides {
  list-style: none;
  padding: 0;
  margin: 0;
  counter-reset: slides;
}

@media screen and (min-width: 120ch) {
  #slides {
    grid-auto-flow: column;
    overflow-x: auto; 
    scroll-snap-type: x mandatory;
  }
}

.slide {
  position: relative;
  counter-increment: slides;
}

@media screen and (min-width: 120ch) {
  .slide {
    width: 100vw;
    height: 100vh;
    scroll-snap-align: center;
    scroll-snap-stop: always;
  }
}

@media (max-width: 120ch) {
  .slide {
    min-height: 80vh;
  }
    
  .slide + .slide {
    border-top: 1px dashed;
  }
}

.slide::before {
  content: counter(slides);
  position: absolute;
  top: 0.25rem;
  left: 0.25rem;
  width: 1.65em;
  height: 1.65em;
  display: grid;
  place-content: center;
  border-radius: 50%;
  font-size: 1.25rem;
  color: hsl(var(--theme-hs), 95%);
  background-color: hsl(var(--theme-hs), 55%);
}

@media (min-width: 120ch) {
  .slide::before {
      top: auto;
      bottom: 1rem;
      left: 1rem;
    }
}

[data-topic]::before {
  content: counter(slides) ": " attr(data-topic);
  padding: 0.25em 0.4em;
  width: auto;
  border-radius: 0.5rem;
}

.slide--text,
.slide--title {
  place-content: center;
}

.slide--title {
  background-image: 
    linear-gradient(125deg, 
      hsl(var(--theme-hs), 95%), 
      hsl(var(--theme-hs), 75%)
    );
}

@media screen and (min-width: 120ch) {
  .slide--demo {
    grid-template-columns: fit-content(85ch) 1fr;
  }
}

.slide--style-only {
  place-content: center;
  
  .style {
    padding-inline: 3rem;
    border-radius: 1rem;
  }
}

h1, h2 {
  line-height: 1.1;
}

a {
  color: inherit;
}

.content {
  padding: 2rem;
  font-size: 1.5rem;
  line-height: 1.5;
  width: calc(100vw - 2rem);
}

.content * + * {
  margin-top: 0.5em;
}

@media screen and (min-width: 120ch) {
  .content {
    width: unset;
    max-width: 45ch;
  }
}

.style {
  display: grid;
  align-items: center;
  background-color: hsl(var(--theme-hs), 5%);
  padding-inline: max(5vw, 2rem) 3rem;
  font-size: 1.35rem;
  overflow-y: hidden;
  resize: horizontal;
}

style {
  --line-height: 1.65em;
  --highlight-start: calc(2 * var(--line-height));
  --lines: calc(var(--highlight-start) + var(--num-lines, 1) * var(--line-height));
  
  display: block;
  outline: none;
  font-family: Consolas, Monaco, "Andale Mono", "Ubuntu Mono", monospace;
  color: hsl(var(--theme-hs), 75%);
  background: none;
  white-space: pre;
  line-height: 1.65;
  tab-size: 2;
  hyphens: none;
  -webkit-text-fill-color: transparent;
  -webkit-background-clip: text; 
  background-image: linear-gradient(
    hsl(var(--theme-hs), 75%) 0 var(--highlight-start),
    hsl(var(--theme-hs), 90%) var(--highlight-start) var(--lines),
    hsl(var(--theme-hs), 75%) var(--lines) 100%
  );
}

.highlight--rule-only {
  --highlight-start: calc(1 * var(--line-height))
}

.highlight--none {
  background-image: none;
  background-color: currentColor;
}

.demo {
  padding: 2rem;
}

.demo-overflow {
  overflow-y: auto;
  max-height: 100vh;
}

/* Extra demo presentation styles */
.modern-container {
  gap: var(--gap);
}

button {
  all: unset;
  border: 1px solid;
  padding: 0.25em 0.5em;
  border-radius: 0.25rem;
  cursor: pointer;
  font-size: 2.5rem;
  justify-self: center;
  
  &:hover {
    background-color: hsl(260, 85%, 90%);
  }
}

[type="radio"],
[type="checkbox"] {
  width: 2rem;
  height: 2rem;
}

li li {
  list-style: disc;
}

.note {
  border: 2px dashed hsl(260, 85%, 65%);
  color: hsl(260, 85%, 25%);
  font-size: 1.35rem;
  padding: 0.25rem 1rem;
  line-height: 1.5;
  margin-top: 4rem;
}

p + :is(p, h2) {
  margin-top: 1.5em;
}

a:focus {
  outline: 2px solid currentColor;
  outline-offset: 1px;
}

.icons {
  display: flex;
  gap: 1rem;
}

.icon {
  padding: 0 !important;
  border-radius: 50%;
  aspect-ratio: 1;
  font-size: 1rem;
}

.grid {
  align-self: start;
}

::selection {
  -webkit-text-fill-color: hsl(260, 85%, 5%);
  color: hsl(260, 85%, 5%);
  background-color: hsl(260, 85%, 95%);
}
!

JS
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999px

Console