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HTML 

              
                <div class="wrapper">
  <h1>JavaScript pairs Game</h1>
  <h3>Click any card to begin</h3>
  <p><span id="seconds">00</span>:<span id="tens">00</span></p>
  <p id ="text"></p>
  <div id="container">

  </div>
</div>
!

CSS 

              
                /* Variabes */  
$orange: #ffa600;
$green: #c1d72e;
$blue: #82d2e5;
$grey: #f3f3f3;
$white: #fff;
$base-color:$blue ;


/* Mixin's */  
@mixin transition {
  -webkit-transition: all 0.5s ease-in-out;
  -moz-transition: all 0.5s ease-in-out;
  transition: all 0.5s ease-in-out;
}

@mixin corners ($radius) {
  -moz-border-radius: $radius;
  -webkit-border-radius: $radius;
  border-radius: $radius; 
  -khtml-border-radius: $radius; 
}

body {
  background:$base-color;
  font-family: "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif; 
  height:100%;
  color: $white;
  text-align: center;
}


h1, h2 {
  font-family: 'Roboto', sans-serif;
  font-weight: 100;
  font-size: 2.6em;
  text-transform: uppercase;
}

h3 {
  font-family: 'Roboto', sans-serif;
  font-weight: 100;
  font-size: 1.4em;
  text-transform: uppercase;
}

#seconds, #tens{
  font-size:2em;
}

button{
  @include corners (5px);
  background:$base-color;
  color:$white;
  border: solid 1px $white;
  text-decoration:none;
  cursor:pointer;
  font-size:1.2em;
  padding:18px 10px;
  width:180px;
  margin: 10px;
  outline: none;
 
    &:hover {
    	@include transition;
    	background:$white;
    	border: solid 1px $white;
    	color:$base-color;
  	}
    
}


#container {
  width: 630px;
  margin: 10px auto;

  &:after {
    content: "";
    display: table;
    clear: both;
  }
  
}

[data-view="card"] {
  transform: rotateY(180deg);
  width: 100px;
  height: 140px;
  border: solid 1px #d3cece;
  border-radius: 5px;
  float: left;
  margin: 10px;
  cursor: pointer;
  background:
  linear-gradient(135deg, $grey 22px, $white 22px, $white 24px, transparent 24px, transparent 67px, $white 67px, $white 69px, transparent 69px),
  linear-gradient(225deg, $grey 22px, $white 22px, $white 24px, transparent 24px, transparent 67px, $white 67px, $white 69px, transparent 69px)0 64px;
  background-color: $grey;
  background-size: 64px 128px
}

.flipped {
  transition: 0.6s;
	transform-style: preserve-3d;
  position: relative;
	transform: rotateY(0deg);
}

.reverse {
  transition: 0.6s;
	transform-style: preserve-3d;
  position: relative;
	transform: rotateY(180deg);
}

.correct {
  opacity: .5;
  cursor: default;
	transform-style: preserve-3d;
  position: relative;
	transform: rotateY(0deg);
}

/* Icons */
$cards: sass, gulp, grunt, git, css;
       
@each $card in $cards  {

  .correct[data-item="#{$card}"],
  .flipped[data-item="#{$card}"]{
    background:url("https://cathydutton.co.uk/images/tech/#{$card}.jpg") left center no-repeat $white;
    background-size: contain;
  }

}
!

JS 

              
                var myCards = document.getElementById('container');
var resultsArray = [];
var counter = 0;
var text = document.getElementById('text');
var seconds = 00; 
var tens = 00; 
var appendTens = document.getElementById("tens");
var appendSeconds = document.getElementById("seconds");
var Interval ;
var images = [
  'sass', 
  'git', 
  'gulp', 
  'css', 
  'grunt'
];

var clone = images.slice(0); // duplicate array
var cards = images.concat(clone); // merge to arrays 

// Shufffel function
function shuffle(o){
  for(var j, x, i = o.length; i; j = Math.floor(Math.random() * i), x = o[--i],   o[i] = o[j], o[j] = x);
  return o;
}
shuffle(cards);

for (var i = 0; i < cards.length; i++) {
  card = document.createElement('div');
  card.dataset.item = cards[i];
  card.dataset.view = "card";
  myCards.appendChild(card);
     
  card.onclick = function () {
   
    if (this.className != 'flipped' && this.className != 'correct'){
        this.className = 'flipped';
        var result = this.dataset.item;
        resultsArray.push(result);
        clearInterval(Interval);
        Interval = setInterval(startTimer, 10);
    }
  
    if (resultsArray.length > 1) {

      if (resultsArray[0] === resultsArray[1]) {
        check("correct");
        counter ++;
        win();
        resultsArray = [];
      } else {
        check("reverse");
        resultsArray = [];
      }
      
    }
    
  }
   
};


var check = function(className) {
  
  var x = document.getElementsByClassName("flipped");
  setTimeout(function() {

    for(var i = (x.length - 1); i >= 0; i--) {
      x[i].className = className;
    }
     
  },500);
   
}

var win = function () {

  if(counter === 5) {
    clearInterval(Interval);
    text.innerHTML = "Your time was " + seconds + ":" + tens;
  } 
  
}
     
function startTimer () {
  tens++; 
    
  if(tens < 9){
    appendTens.innerHTML = "0" + tens;
  }
    
  if (tens > 9){
    appendTens.innerHTML = tens;
      
  } 
    
  if (tens > 99) {
    seconds++;
    appendSeconds.innerHTML = "0" + seconds;
    tens = 0;
    appendTens.innerHTML = "0" + 0;
  }
    
  if (seconds > 9){
    appendSeconds.innerHTML = seconds;
  }
  
}
!
999px

Console