<h1>Pure CSS Tic-Tac-Toe</h1>

<p>Pink (X's) v. Green (O's) &mdash; Each team has 5 seconds to make a move!</p>

<div class="gameboard">
  <div class="team--o">
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <span class="message--o"></span>
  </div>
  
  <div class="team--x">
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <input type="checkbox"/>
    <span class="message--x"></span>
  </div>
</div>
$green: #71e571;
$pink: #ff64d1;

// basic example: https://codepen.io/una/pen/xVOpRr

// all of the cases
:checked + :checked + :checked ~ .message--x:after,
:checked + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked ~ .message--x:after,
:not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked ~ .message--x:after,
:not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked ~ .message--x:after,
:not(:checked) + :not(:checked) + :checked + :not(:checked) + :checked + :not(:checked) + :checked ~ .message--x:after,
:checked + :not(:checked) + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :not(:checked)+ :checked ~ .message--x:after,
{
  @extend %win-message;
  content: "X Wins!";
  background: $pink;
}

// O cases

:checked + :checked + :checked ~ .message--o:after,
:checked + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked ~ .message--o:after,
:not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked ~ .message--o:after,
:not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :checked ~ .message--o:after,
:not(:checked) + :not(:checked) + :checked + :not(:checked) + :checked + :not(:checked) + :checked ~ .message--o:after,
:checked + :not(:checked) + :not(:checked) + :not(:checked) + :checked + :not(:checked) + :not(:checked) + :not(:checked)+ :checked ~ .message--o:after,
{
  @extend %win-message;
  content: "O Wins!";
  background: $green;
}

%win-message {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 100%;
  z-index: 10;
  font-size: 3em;
  line-height: 5.3;
  font-weight: 800;
}

// once it's checked you can't uncheck it
:checked {
  pointer-events: none;
}

body {
  text-align: center;
  font-family: 'Open Sans', 'Helvetica', 'Arial', sans-serif;
  color: #333;
}

.team--x {
  counter-reset: count-x;
}

.team--o {
  counter-reset: count-o;
}

.team--x :checked {
  counter-increment: count-x;
}

.team--o :checked {
  counter-increment: count-o;
}

.total-count--x::after {
  content: counter(count-x);
}

.total-count--o::after {
  content: counter(count-o);
}

// boxes overlap
.team--x,
.team--o {
  position: absolute;
  top: 0;
  left: 0;
}

// just page styling:

body {
  text-align: center;
  background: #eee;
  position: relative;
  padding: 3em;
}

h1 {
  font-size: 1.5em;
  font-weight: 800;
  margin-bottom: .5em;
}

p {
  font-size: 1em;
  line-height: 1.5;
  max-width: 18em;
  margin: 0 auto;
}

// styling the checks

$box-size: 8em;

input {
  border: none;
  display: block;
  float: left;
  margin: 0;
  background-color: none;
  appearance: none;
  width: $box-size;
  height: $box-size;
  
  .team--x & {
    outline: 1px solid $pink;
  }

  .team--o & {
    outline: 1px solid $green;
  }
}

.gameboard {
  display: block;
  position: absolute;
  width: $box-size*2.25;
  margin: 1.5em auto;
  left: 0;
  right: 0;
}

:checked {
  &:after {
    line-height: .75;
    font-size: $box-size;
    text-align: center;
    width: 1em;
    height: 1em;
    display: block;
    
    .team--x & {
      background-color: $pink;
      content: 'x';
    }
    
    .team--o & {
      background-color: $green;
      content: 'o';
    }
  }
}

// Animating a Set-Timeout for Turn switching

@keyframes turn-switcher {
  0% {
    z-index: 1;
    pointer-events: none;
  }
  1% {
    z-index: -1;
    pointer-events: all;
  }
}

// applying the animation:
.team--x {
  animation: turn-switcher 10s forwards linear infinite;
  animation-delay: 5s;
}

External CSS

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