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HTML

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About the <head>

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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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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <header>
  <nav>
    <a href="#">Super App 3000</a>
    <ul class="menu">
      <li>Choose Grid Layout:</li>
      <li>
        <button class="is-current js-layout-button" type="button" data-layout-toggle="1">
          Three columns
        </button>
      </li>
      <li>
        <button class="js-layout-button" type="button" data-layout-toggle="2">
          Two columns
        </button>
      </li>
      <li>
        <button class="js-layout-button" type="button" data-layout-toggle="3">
          One column
        </button>
      </li>
    </ul>
  </nav>
</header>

<main class="grid js-grid" data-layout="1">
  <div id="module_1"><span>1</span></div>
  <div id="module_2"><span>2</span></div>
  <div id="module_3"><span>3</span></div>
</main>

<footer>
  <p>
    &copy; #currentyear &ndash;
    <a href="https://www.bshow.co/">Bobby Showalter</a>
  </p>
</footer>
!

CSS 

              
                /**
 * Grid Layout magic!
 */
@media screen and (min-width: 60rem) {
  /* parent grid settings */
  .grid {
    display: grid;
    align-items: start;
    grid-column-gap: 1rem;
  }
  
  /* layout 1 styles */
  .grid[data-layout="1"] {
    grid-template: min-content / 15rem 1fr 15rem;
  }
  
  /* layout 2 styles */
  .grid[data-layout="2"] {
    grid-template: repeat(2, min-content) / 1fr 15rem;
  }
  
  .grid[data-layout="2"] #module_1 {
    grid-area: 1 / 1 / 2 / 2;
  }
  
  .grid[data-layout="2"] #module_2 {
    grid-area: 2 / 1 / 3 / 2;
  }
  
  .grid[data-layout="2"] #module_3 {
    grid-area: 1 / 2 / 3 / 3;
  }
  
  /* layout 3 styles */
  .grid[data-layout="3"] {
    grid-template: repeat(3, min-content) / 100%;
  }
}



/**
 * Beautification stuff
 */

/* |Variables */
:root {
  /* colors */
  --c-white: #fbfbfb;
  --c-light-gray: #dfe6e9;
  --c-gray: #b2bec3;
  --c-shadow: #636e7255; /* #rrggbbaa */
  --c-text: #2d3436;
  --c-red: #d6303155;
  --c-green: #00b89455;
  --c-blue: #0984e355;
}

/* |Styles */
html {
  background-color: var(--c-light-gray);
  box-sizing: border-box;
  color: var(--c-text);
  font-family: 'Work Sans', sans-serif;
}

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

html,
body {
  height: 100%;
}

body {
  display: grid;
  grid-template-rows: min-content 1fr min-content;
}

header,
footer {
  background-color: var(--c-gray);
  border: 2px solid var(--c-shadow);
}

footer p {
  margin: 0;
  padding: 1rem;
}

footer p a {
  color: var(--c-text);
  font-weight: 700;
}

nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem;
}

nav a {
  color: var(--c-text);
  font-size: 1.5rem;
  font-weight: 700;
}

.menu {
  display: flex;
  align-items: center;
  list-style: none;
  margin: 0;
  padding-left: 0;
}

.menu li + li {
  margin-left: 1rem;
}

.menu button {
  background: transparent;
  border: 1px solid var(--c-text);
  border-radius: 3px;
  color: var(--c-text);
  font-family: inherit;
  padding: .25rem .75rem;
  transition:
    background-color 250ms ease-out,
    color 250ms ease-out;
}

.menu button:hover {
  background-color: var(--c-light-gray);
}

.menu button.is-current {
  background-color: var(--c-text);
  color: var(--c-light-gray);
}

main {
  margin: 2.25rem 0;
  padding: 0 1rem;
}

.grid div {
  border-radius: 3px;
  box-shadow: 0 1px 3px var(--c-shadow);
  margin-bottom: 1rem;
  padding: 1rem;
}

.grid div span {
  display: block;
  font-size: calc(1vw + 1.5rem);
  font-weight: 900;
  padding: 1rem 1.5rem;
}

#module_1,
#module_1 span {
  background-color: var(--c-red);
  min-height: 200px;
}

#module_2,
#module_2 span {
  background-color: var(--c-green);
  min-height: 600px;
}

#module_3,
#module_3 span {
  background-color: var(--c-blue);
  min-height: 350px;
}
!

JS 

              
                const layoutButtons = document.querySelectorAll('.js-layout-button');
const mainGrid = document.querySelector('.js-grid');

function changeLayout(e) {
  e.preventDefault();
  layoutButtons.forEach(button => {
    button.classList.remove('is-current');
  });
  let layoutChoice = this.getAttribute('data-layout-toggle');
  mainGrid.setAttribute('data-layout', layoutChoice);
  this.classList.add('is-current');
}

layoutButtons.forEach(button => button.addEventListener('click', changeLayout));
!
999px

Console