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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

            
              .container
  #start
  form#instruction-screen.overlay
    div
      h2 How to Play Concentration
      p Click a card to turn it over. Turn over matching pairs of cards to remove them from the deck. The game is over once all the cards are removed.
      .btn-container
        input(type="checkbox" required="required")
  .timer-container.top-corner Time: <span class="elapsed-time"></span>

  - var list = [['a1','a2'],['b1','b2'],['c1','c2'],['d1','d2'],['e1','e2'],['f1','f2'],['g1','g2'],['h1','h2'],['i1','i2']];
  each val in list
    div(id=val[0] class="target")
    div(id=val[1] class="target")
    form(class="card-body "+val[0] id="form-"+val[0])
      input(type="checkbox" required="required")
    form(class="card-body "+val[1] id="form-"+val[1])
      input(type="checkbox" required="required")
  div(class="overlay game-over")
    div
      h2 Game over
      p You finished in <span class="elapsed-time"></span> seconds.

  article
    each val in list
      div(class="card-holder card-holder-"+val[0])
        span(id=val[0]+"f" class="last-click")
        a(href="#"+val[0]+"f" class="inactive-card card-body "+val[0])
        a(href="#"+val[0] class="first-card card-body "+val[0])
          .card-container
            .front
            .back
      div(class="card-holder card-holder-"+val[1])
        span(id=val[1]+"f" class="last-click")
        a(href="#"+val[1]+"f" class="inactive-card card-body "+val[1])
        a(href="#"+val[1] class="first-card card-body "+val[1])
          .card-container
            .front
            .back
            
          
!
            
              $pairs : (
  ('a1', 'a2', 'a'),
  ('b1', 'b2', 'b'),
  ('c1', 'c2', 'c'),
  ('d1', 'd2', 'd'),
  ('e1', 'e2', 'e'),
  ('f1', 'f2', 'f'),
  ('g1', 'g2', 'g'),
  ('h1', 'h2', 'h'),
  ('i1', 'i2', 'i')
);

$all_coords: (
  (13, 13), (45, 13), (77, 13), (109, 13), (141, 13), (173, 13), 
  (13, 61), (45, 61), (77, 61), (109, 61), (141, 61), (173, 61),  
  (13, 109), (45, 109), (77, 109), (109, 109), (141, 109), (173, 109)  
);


$coords_order : ();
$used_indexes : () !global;

@function contains($list,$var) {
  $_out: false;
  @each $item in $list { @if $item == $var { $_out: true; } }
  @return $_out;
}

@function get_random_index($list){
  $pos: random(length($list));
  @if contains($used_indexes, $pos){
    $pos:get_random_index($list);
  } @else{
    $used_indexes:join($used_indexes, $pos) !global;
  }
  @return $pos;
}

@function randomize_list($list){
  $coords_order:();
  @for $i from 0 to length($list){  
    $index:get_random_index($list); 
    $coords_order:join($index,$coords_order);
  }
  @return $coords_order; 
}

$coords_order:randomize_list($all_coords);
// @warn $coords_order;

// z-indexes
$z_i_form: 100;
$z_i_card_holder: 200;
$z_i_first_card: 500;
$z_a_form: 500;
$z_a_inactive_card: 600;
$z_a_first_card: 800;

$pixel: var(--pixel);

$max_time : 181; // counter

@keyframes flip_front_back {
  0%{
    transform: rotateY(0deg);
  }
  33%, 67%{
    transform: rotateY(180deg);
  }
  100%{
    transform: rotateY(0deg);
  }
}

@keyframes flip_front {
  0%, 33%{
    opacity:1;
  }
  66%, 100%{
    opacity:0;
  }
}

@keyframes clock{
  @for $i from 0 to $max_time {
    #{($i/($max_time))*100}%{
      content:'#{$i}';
    }
  }
  100%{
    content:'> #{($max_time - 1)}';
  }
}

html, body{
  padding:0;
  margin:0;
}

body{
  font-family: 'Montserrat', sans-serif;
  background:#111;
  --pixel:0.46vw;
  line-height:1.33;
  @media (min-aspect-ratio: 4/3) {
    --pixel:0.6vh;
  }
}

form{
  position:relative;
  z-index:$z_i_form;
}
.card-holder{
  z-index:$z_i_card_holder;
  position:relative;
}

h2{
  margin:0;
}

p{
  margin:0.5rem 0 1.25rem;
}


/* ************* */
/*     timer     */
/* ************* */

.timer-container{
  color:#fff;
  position: absolute;
  top:0;
  right:0;
  padding:0 calc(var(--pixel) * 12) 0 0;
  .elapsed-time{
    display:inline-block;
    text-align:right;
    min-width:20px;
  }
}

.elapsed-time:before{
  display:inline-block;
  content:'0';
  animation:clock #{$max_time}s forwards;
}

.overlay{
  position:absolute;
  top:0;
  left:0;
  width:100%;
  height:100%;
  color:#fff;
  display: flex;
  align-items: center;
  justify-content: center;
  background-color:#111;
  z-index:2;
  text-align:center;
  box-sizing: border-box;
  padding:20px;
  z-index:1000;
  &:valid{
    display:none;   
  }
  .btn-container{
    width: 90px;
    margin: 0 auto;
    position:relative;
  }
  input[type="checkbox"]{
    -webkit-appearance: none;
    position:absolute;
    top:0;
    left:0;
    cursor: pointer;
    &:after{
      content:'Play';
      display: inline-block;
      text-decoration: none;
      color: #fff;
      border: 3px solid #fff;
      padding: 10px 12px;
      font-size:16px;
      width:100%;
      transition: 0.25s all;
      bottom:auto;
      text-align:center;
    }
    &:hover:after{
      color:#0095ff;
      border-color:#0095ff;
    }
  }
}

#instruction-screen:invalid ~ .timer-container .elapsed-time:before, 
#instruction-screen:invalid ~ .game-over .elapsed-time:before{
  animation-play-state: paused;
}

@media not all and (min-resolution:.001dpcm) { 
  // hack to hide the time from safari, which doesn't
  // allow us to animate the content property
  .timer-container, .game-over p{
    display:none;
  }
}
.overlay.game-over{
  opacity:0;
  pointer-events: none;
  transition: 1s auto;
}

form.card-body:valid ~ 
form.card-body:valid ~ 
form.card-body:valid ~ 
form.card-body:valid ~ 
form.card-body:valid ~ 
form.card-body:valid ~ 
form.card-body:valid ~ 
form.card-body:valid ~ 
form.card-body:valid ~ 
.overlay.game-over{
  opacity:1;
  pointer-events: auto;
  .elapsed-time:before{
    animation-play-state: paused;    
  }
}

/* ************* */
/*     cards     */
/* ************* */

.card-body{
  width:calc(#{$pixel}  * 22);
  height:calc(#{$pixel} * 32);
  display:inline-block;
  position:absolute;
  transition:0.5s;
}

.card-container, .front, .back{
  position:absolute;
  top:0;
  left:0;
  width:calc(#{$pixel}  * 22);
  height:calc(#{$pixel} * 32);
  image-rendering: pixelated;
  background-size:cover;
  -webkit-transform-style: preserve-3d;
  -webkit-backface-visibility: hidden;
}

.card-container{
  transition: 1s all;
  transition-delay: 1s;
  transform:rotateY(0deg);
  animation-timing-function: steps(10, end);
}

.back{
  background-image:url('https://s3-us-west-2.amazonaws.com/s.cdpn.io/67732/card-back.gif');
}

.front{
  background-color:#ffc4b7;
  z-index:2;
  transform: rotateY(180deg);
}

.first-card{
  z-index:$z_i_first_card;
}

.container{
  background-color:#111;
  width:calc(#{$pixel} * 208);
  height:calc(#{$pixel} * 154);
  position: absolute;
  top:50%;
  left:50%;
  transform: translate(-50%, -50%);
}

form.card-body{
  z-index:$z_i_form;
  input[type="checkbox"]{
    -webkit-appearance:none;
    &:after{
      cursor: pointer;
      content:'';
      display:block;
      width:100%;
      height:100%;
      position: absolute;
      top:0;
      left:0;
    }
  }
}

$pos:1;
@each $pair in $pairs { 
  // x,y positioning
  .#{nth($pair, 1)}, .#{nth($pair, 2)}{
    .front{
      background-image:url('https://s3-us-west-2.amazonaws.com/s.cdpn.io/67732/card-#{nth($pair, 3)}.gif')
    }
  }
  .#{nth($pair, 1)}{
    $coords : nth($all_coords,nth($coords_order, $pos));
    left:calc(#{$pixel} * #{nth($coords,1)});
    top:calc(#{$pixel} * #{nth($coords,2)});
    $pos:$pos+1;
  }
  
  .#{nth($pair, 2)}{
    $coords : nth($all_coords,nth($coords_order, $pos));
    left:calc(#{$pixel} * #{nth($coords,1)});
    top:calc(#{$pixel} * #{nth($coords,2)});
    $pos:$pos+1;
  }

  ##{nth($pair, 1)}:target,
  ##{nth($pair, 2)}:target{ 
    // move all reset cards to the top
    ~ article .card-holder .inactive-card{
      z-index:$z_a_inactive_card;
    }

    // move the current cards reset to the bottom
    ~ #form-#{nth($pair, 1)}:valid,
    ~ #form-#{nth($pair, 2)}:valid{
      ~ article .card-holder .inactive-card{
        z-index:1;
      }
    }
  }

  // flip over the current card
  ##{nth($pair, 1)}:target ~ article .card-holder-#{nth($pair, 1)},
  ##{nth($pair, 2)}:target ~ article .card-holder-#{nth($pair, 2)}{
    z-index:$z_a_form;
    .card-body .card-container{
      transition-delay: 0s;
      transform:rotateY(180deg);
    }
  }

  // move the selected cards input to the top
  ##{nth($pair, 1)}:target ~ #form-#{nth($pair, 2)},
  ##{nth($pair, 2)}:target ~ #form-#{nth($pair, 1)}{
    z-index:$z_a_form;
    input{
      z-index:$z_a_form;
    }
  }
  
  // matched cards
  #form-#{nth($pair, 1)}:valid,
  #form-#{nth($pair, 2)}:valid{
    ~ article .card-holder-#{nth($pair, 1)},
    ~ article .card-holder-#{nth($pair, 2)}{
      .card-body {
        animation:flip_front 3s forwards;
        pointer-events: none;
        .card-container{
          transform: rotateY(180deg);
          animation:none;
          transition-delay:0s;
        }
      }
    }
  }
}

.last-click:target ~ .card-body .card-container{
  background-color:#ccc;
  animation:flip_front_back 3s forwards;
}

            
          
!
999px
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