<main>
  <h2>Understanding Complex Ordering: <code>order</code></h2>
  <p>The differently-colored flex item changes its order depending on what's selected. The rest of the items have an <code>order</code> value equal to the numbers shown.</p>
  <div class="btns">
    <label for="one">1 <input type="radio" name="order"  value="one" id="one" checked></label>
    <label for="two">2 <input type="radio" name="order"  value="two" id="two"></label>
     <label for="three">3 <input type="radio" name="order"  value="three" id="three"></label>
     <label for="four">4 <input type="radio" name="order"  value="four" id="four"></label>
     <label for="five">5 <input type="radio" name="order"  value="five" id="five"></label>
     <label for="six">6 <input type="radio" name="order"  value="six" id="six"></label>
     <label for="seven">7 <input type="radio" name="order"  value="seven" id="seven"></label>
     <label for="eight">8 <input type="radio" name="order"  value="eight" id="eight"></label>
  </div>
    <div class="container">
      <div class="item one">1</div>
      <div class="item two">2</div>
      <div class="item three">3</div>
      <div class="item four">4</div>
      <div class="item five extra">5</div>
      <div class="item six">6</div>
      <div class="item seven">7</div>
      <div class="item eight">8</div>
      <div class="item nine">9</div>
      <div class="item ten">10</div>
      <div class="item eleven">11</div>
      <div class="item twelve">12</div>
    </div>
  <div class="dir">
    <label for="ltr">left-to-right <input type="radio" value="ltr" name="direction" id="ltr" checked></label>
    <label for="rtl">right-to-left <input type="radio" value="rtl" name="direction" id="rtl"></label>
  </div>
</main>

body {
  font-family: Arial, sans-serif;
  font-size: 1.3em;
  padding: 0 2em 3em;
  line-height: 1.4;
}

main {
  max-width: 800px;
  margin: 0 auto;
}

h2 {
  margin-top: 14px;
  text-align: center;
}

code {
  font-family: Consolas, monospace;
  background: #ccc;
  padding: 1px 3px;
}

.btns {
  padding-bottom: 1em;
  text-align: center;
}

.dir {
  text-align: center;
}

label {
  margin-right: 1.3em;
  padding: 8px;
}

.container {
  min-height: 500px;
  border: solid 2px;
  margin-bottom: 1em;
  background: #b2d5ff;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
}

.ltr {
  direction: ltr;
}

.rtl {
  direction: rtl;
}

.one {
  order: 1;
}

.two {
  order: 2;
}

.three {
  order: 3;
}

.four {
  order: 4;
}

.five {
  order: 5;
}

.six {
  order: 6;
}

.seven {
  order: 7;
}

.eight {
  order: 8;
}

.nine {
  order: 9;
}

.ten {
  order: 10;
}

.eleven {
  order: 11;
}

.twelve {
  order: 12;
}

.item {
  min-width: 15%;
  background: #007ed3;
  min-height: 100px;
  margin: .060em;
  border: solid 2px #305077;
  text-align: center;
  font-size: 3em;
  color: white;
  font-weight: bold;
  line-height: 1.4;
}

.extra {
  background: pink;
}

let btns = document.querySelector('.btns').querySelectorAll('input'),
    dirs = document.querySelector('.dir').querySelectorAll('input'),
    container = document.querySelector('.container'),
    extra = document.querySelector('.extra');

for (i of btns) {
  (function(i) {
    i.addEventListener('click', function() {
      clearClasses(extra, btns);
      extra.classList.add(i.value);
    }, false);
  })(i);
}

for (i of dirs) {
  (function(i) {
    i.addEventListener('click', function() {
      clearClasses(container, dirs);
      container.classList.add(i.value);
    }, false);
  })(i);
}

function clearClasses (el, cl) {
  for (i of cl) {
    el.classList.remove(i.value);
  }
}