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HTML

              
                %button.night-button
%header
  %h1 Randomising Flex Order of Items
  %p Just a random thing where my colleague said "it'd be really good if we could do this", so I did.
%main
  %h2 Showing first of all that the randomisation can be done.
  %button.randomise-button Re-randomise
  .container
    -# Change the numbers in the range below (1..25) to see the results!
    - (1..25).each do |i|
      %div.item{:id => "item-#{i}"} #{i}
  %h2 Actual Application
  %p This is where we had a range of vendor logos to choose from, but only had room to display a certain subset of them depending on screen size, and of course we didn't want them to always be the same ones - someone viewing on a mobile might think we supply kit from 3 different vendors and that's it!
  %button.randomise-button Re-randomise
  .container-app
    - (1..25).each do |i|
      %div.item{:id => "item-#{i}"} #{i}
  %p You will notice that the above row still displays random numbers between the 2 numbers you have chosen, (if you're in the full view on CodePen, it defaults to 1 and 25) but it only displays a subset of them, using overflow: hidden to hide the rest.
%footer
  %p Gavin Sykes 2020
              
            
!

CSS

              
                $white: #eef;
$black: #080808;

* {
  font-family: -apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen,Ubuntu,Cantarell,Fira Sans,Droid Sans,Helvetica Neue,sans-serif;
  box-sizing: border-box;
}

html {
  padding: 0;
  color: $black;
  background-color: $white;
  min-height: 100vh;
  max-width: 100vw;
}
body {
  margin: 0;
  padding: 0;
  max-width: 100vw;
  min-height: 100vh;
  display: grid;
  grid-template-rows: auto auto 1fr auto auto;
  grid-template-columns: 1fr;
  grid-template-areas:
    "header"
    "nav"
    "main"
    "footer";
  &.night {
    color: $white;
    background-color: $black;
  }
}
.night-button {
  position: fixed;
  bottom: 0;
  right: 0;
  font-weight: bold;
  background-color: $black;
  color: $white;
  border: none;
  padding: 1rem;
  border-top-left-radius: 1rem;
}
.night .night-button {
  background-color: $white;
  color: $black;
}
header {
  grid-area: header;
  padding: 0.5rem;
}
main {
  grid-area: main;
  padding: 0.5rem;
}
footer {
  grid-area: footer;
  padding: 0.5rem;
}
.container {
  display: flex;
  flex-flow: row wrap;
  justify-content: space-around;
}
.container-app {
  @extend .container;
  height: 110px;
  overflow: hidden;
}
.randomise-button {
  border-radius: 1rem;
  border: none;
  padding: 1rem;
  background-color: orange;
  color: $black;
  margin: 10px;
  text-align: center;
}
.night .randomise-button {
  background-color: darkred;
}
.item {
  @extend .randomise-button;
  width: 100px;
  height: 100px;
  padding: 0;
  font-weight: 700;
  font-size: 3rem;
  color: $white;
}
.night .item {
  color: $black;
  background-color: darkred;
}
              
            
!

JS

              
                /* --- NIGHT MODE FUNCTIONS --- */
const keyElems = {
  html        : document.querySelector('body'),
  nightButton : document.querySelector('.night-button')
};
function toggleNight() {
  setNight(!isNight());
}
const isNight = () => keyElems.html.classList.contains('night');
function setNight(night) {
  if (night) {
    keyElems.html.classList.add('night');
    keyElems.nightButton.textContent = `Day Mode`;
  } else {
    keyElems.html.classList.remove('night');
    keyElems.nightButton.textContent = `Night Mode`;
  }
}
function checkNightOnLoad() {
  let h = new Date().getHours();
  if (h < 7 || h > 18) {
    setNight(true);
  } else {
    setNight(false);
  }
}
checkNightOnLoad();
keyElems.nightButton.addEventListener('click',toggleNight);
/* --- END OF NIGHT MODE FUNCTIONS --- */

class nightMode {
  constructor(els) {
    this.html = els.html;
    this.nightButton = els.nightButton;
  }
}

const randomiseFlexOrder = querySelector => {
  [...querySelector].map((c,i,a) => c.style.order = Math.floor(Math.random() * a.length + 1));
};
randomiseFlexOrder(document.querySelectorAll('.item'));
Array.from(document.querySelectorAll('.randomise-button')).map(i => i.addEventListener('click',() => randomiseFlexOrder(document.querySelectorAll('.item'))));
              
            
!
999px

Console