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HTML

              
                <input type="checkbox" id="difficulty" checked />
<input type="checkbox" id="sound" />
<input type="checkbox" id="first" />

<input type="checkbox" id="start" />

<form id="tictactoe">  
  <input type="radio" name="cell-0" id="cell-0-x" />
  <input type="radio" name="cell-0" id="cell-0-o" />
  <input type="radio" name="cell-1" id="cell-1-x" />
  <input type="radio" name="cell-1" id="cell-1-o" />
  <input type="radio" name="cell-2" id="cell-2-x" />
  <input type="radio" name="cell-2" id="cell-2-o" />
  <input type="radio" name="cell-3" id="cell-3-x" />
  <input type="radio" name="cell-3" id="cell-3-o" />
  <input type="radio" name="cell-4" id="cell-4-x" />
  <input type="radio" name="cell-4" id="cell-4-o" />
  <input type="radio" name="cell-5" id="cell-5-x" />
  <input type="radio" name="cell-5" id="cell-5-o" />
  <input type="radio" name="cell-6" id="cell-6-x" />
  <input type="radio" name="cell-6" id="cell-6-o" />
  <input type="radio" name="cell-7" id="cell-7-x" />
  <input type="radio" name="cell-7" id="cell-7-o" />
  <input type="radio" name="cell-8" id="cell-8-x" />
  <input type="radio" name="cell-8" id="cell-8-o" />

  <div id="menu" class="scrim">
    <div class="center">
      <h1>CSS Tic-Tac-Toe</h1>
      <div>
        <h2>Difficulty</h2>
        <div class="toggle-group">
          <span>Beginner</span>
          <label for="difficulty" class="toggle"></label>
          <span>Advanced</span>
        </div>
        <!-- Soon...
        <h2>Sound</h2>
        <div class="toggle-group">
          <span>Off</span>
          <label for="sound" class="toggle"></label>
          <span>On</span>
        </div>
        -->
        <h2>First turn</h2>
        <div class="toggle-group">
          <span>Player</span>
          <label for="first" class="toggle"></label>
          <span>Computer</span>
        </div>
        <label for="start" id="start-button" class="btn">Start Game</label>
      </div>
    </div>
  </div>

  <div id="board" class="center">
    <div class="tile" id="tile-0">
      <label for="cell-0-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-1">
      <label for="cell-1-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-2">
      <label for="cell-2-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-3">
      <label for="cell-3-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-4">
      <label for="cell-4-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-5">
      <label for="cell-5-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-6">
      <label for="cell-6-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-7">
      <label for="cell-7-x"></label>
      <div></div>
    </div>
    <div class="tile" id="tile-8">
      <label for="cell-8-x"></label>
      <div></div>
    </div>
  </div>
  <div id="label-computer" class="btn">
    Computer Move!
    <label for="cell-0-o"></label>
    <label for="cell-1-o"></label>
    <label for="cell-2-o"></label>
    <label for="cell-3-o"></label>
    <label for="cell-4-o"></label>
    <label for="cell-5-o"></label>
    <label for="cell-6-o"></label>
    <label for="cell-7-o"></label>
    <label for="cell-8-o"></label>
  </div>
  <div id="end" class="scrim">
    <div id="message" class="center">
      <div>
        <input type="reset" for="tictactoe" value="Play again" />
      </div>
    </div>
  </div>
</form>

              
            
!

CSS

              
                @import url('https://fonts.googleapis.com/css?family=Mandali|Raleway:900&display=swap');

input[type="radio"],
input[type="checkbox"] {
  position: absolute;
  top: -9999em;
}

#menu {
  display: block;
  background: rgba(0,0,0,0.8);
  text-align: center;
}

#menu > div {
  background: #fff;
  padding: 1rem 2rem;
  border-radius: 10px;
}

.toggle-group {
  display: flex;
}

.toggle-group span { 
  flex: 1; 
  text-align: left;
}

.toggle-group span:nth-of-type(1) {
  text-align: right;
}

.toggle {
  display: inline-block;
  width: 3rem;
  height: 1.5rem;
  background: #ddd;
  vertical-align: bottom;
  margin: 0.33rem 0.5rem;
  border-radius: 1rem;
  position: relative;
  cursor: pointer;
}

.toggle::before {
  content: "";
  position: absolute;
  display: block;
  width: 1rem;
  height: 1rem;
  top: 0.25rem;
  left: 0.25rem;
  background: #000;
  background: #004974;
  border-radius: 100%;
  transition: left 0.25s, background-color 0.25s;
}

.btn {
  width: 100%;
  display: inline-block;
  background: #000;
  color: #fff;
  border-radius: 5px;
  margin-top: 2rem;
  padding: 0.33rem;
  box-sizing: border-box;
  cursor: pointer;
  transition: background-color 0.25s;
}

.btn:hover {
  background: #333;
}

#start:checked ~ form #menu {
  display: none;
}

#difficulty:checked ~ form #menu label[for=difficulty]::before,
#sound:checked ~ form #menu label[for=sound]::before,
#first:checked ~ form #menu label[for=first]::before {
  left: 1.75rem;
  background: #a60011;
}

h1 {
  margin: 0 0 0.5rem 0;
  text-align: center;
  white-space: nowrap;
   color: #004974;
}

h2 {
  font-size: 0.9rem;
  text-transform: uppercase;
  margin: 1.25rem 0 0.1rem 0;
  color: #a60011;
}

html, body {
  font-family: Mandali, Arial, sans-serif;
  font-size: 16px;
}

.center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

#board {
  width: 50vmin;
  height: 50vmin;
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  grid-template-rows: 1fr 1fr 1fr;
}

.tile {
  margin: 5%;
  position: relative;
}

.tile label,
.tile div {
  display: block;
  height: 100%;
  width: 100%;
  position: absolute;
  top: 0;
  left: 0;
  background: rgba(0,0,0,0.10);
  font-family: Raleway, Courier, 'Courier New', Sans, sans-serif;
  font-weight: bolder;
}

.tile div {
  display: none;
  overflow: hidden;
  text-shadow: 0 1px 6px rgba(0,0,0,0.85)
}

@keyframes shadow {
  from { box-shadow: 0 0 0 0 rgba(255,0,0,0); } 
  to { box-shadow: 0 0 10px 4px rgba(255,0,0,0.35); } 
}

#label-computer {
  width: 200px;
  max-width: 50vmin;
  position: absolute;
  top: 80%;
  top: calc(50% + 30vmin);
  left: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
  animation: shadow 0.75s infinite alternate;
}

@keyframes beginnerAnimation {
  from { z-index: 9; }
  to { z-index: 1; }
}

#label-computer label {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  display: block;
  animation: beginnerAnimation 0.9s infinite;
}

#label-computer label:active {
  position:static !important; 
  margin-left: 100% !important;
  background: none !important;
  font-size: 0;
}

#label-computer label:active::before {
    content:"";
    position:absolute;
    top:0;
    right:-50px;
    left:0;
    bottom:0;
    z-index:101;
}

#label-computer label:nth-child(1) { animation-delay: -0.1s; }
#label-computer label:nth-child(2) { animation-delay: -0.2s; }
#label-computer label:nth-child(3) { animation-delay: -0.3s; }
#label-computer label:nth-child(4) { animation-delay: -0.4s; }
#label-computer label:nth-child(5) { animation-delay: -0.5s; }
#label-computer label:nth-child(6) { animation-delay: -0.6s; }
#label-computer label:nth-child(7) { animation-delay: -0.7s; }
#label-computer label:nth-child(8) { animation-delay: -0.8s; }
#label-computer label:nth-child(9) { animation-delay: 0s; }


/* Special cases */
#cell-0-x:checked ~ #cell-4-x:checked ~ #cell-8-o:checked ~ #label-computer label[for='cell-2-o'],
#cell-0-x:checked ~ #cell-4-x:checked ~ #cell-8-o:checked ~ #label-computer label[for='cell-6-o'],
#cell-2-x:checked ~ #cell-4-x:checked ~ #cell-6-o:checked ~ #label-computer label[for='cell-0-o'],
#cell-2-x:checked ~ #cell-4-x:checked ~ #cell-6-o:checked ~ #label-computer label[for='cell-8-o'],
#cell-2-o:checked ~ #cell-4-x:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-0-o'],
#cell-2-o:checked ~ #cell-4-x:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-8-o'],
#cell-0-o:checked ~ #cell-4-x:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-2-o'],
#cell-0-o:checked ~ #cell-4-x:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-6-o'] {
  z-index: 65;
  animation: none;
}

@keyframes miniAnimation {
  from { z-index: 75; }
  to { z-index: 72; }
}

#cell-0-o:not(:checked) ~ #cell-2-o:not(:checked) ~ #cell-4-x:checked ~ #cell-6-o:not(:checked) ~ #cell-8-o:not(:checked) ~ #label-computer label[for='cell-0-o'],
#cell-0-o:not(:checked) ~ #cell-2-o:not(:checked) ~ #cell-4-x:checked ~ #cell-6-o:not(:checked) ~ #cell-8-o:not(:checked) ~ #label-computer label[for='cell-2-o'],
#cell-0-o:not(:checked) ~ #cell-2-o:not(:checked) ~ #cell-4-x:checked ~ #cell-6-o:not(:checked) ~ #cell-8-o:not(:checked) ~ #label-computer label[for='cell-6-o'],
#cell-0-o:not(:checked) ~ #cell-2-o:not(:checked) ~ #cell-4-x:checked ~ #cell-6-o:not(:checked) ~ #cell-8-o:not(:checked) ~ #label-computer label[for='cell-8-o'] {
  z-index: 75;
  animation: miniAnimation 0.4s infinite linear;
}

#cell-0-o:not(:checked) ~ #cell-2-o:not(:checked) ~ #cell-4-x:checked ~ #cell-6-o:not(:checked) ~ #cell-8-o:not(:checked) ~ #label-computer label[for='cell-0-o'] { animation-delay: -0.3s; }
#cell-0-o:not(:checked) ~ #cell-2-o:not(:checked) ~ #cell-4-x:checked ~ #cell-6-o:not(:checked) ~ #cell-8-o:not(:checked) ~ #label-computer label[for='cell-2-o'] {  animation-delay: -0.2s; }
#cell-0-o:not(:checked) ~ #cell-2-o:not(:checked) ~ #cell-4-x:checked ~ #cell-6-o:not(:checked) ~ #cell-8-o:not(:checked) ~ #label-computer label[for='cell-6-o'] { animation-delay: -0.1s; }



#difficulty:checked ~ form #cell-0-x:checked ~ #cell-4-o:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-1-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-4-o:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-3-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-4-o:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-5-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-4-o:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-7-o'],
#difficulty:checked ~ form #cell-2-x:checked ~ #cell-4-o:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-1-o'],
#difficulty:checked ~ form #cell-2-x:checked ~ #cell-4-o:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-3-o'],
#difficulty:checked ~ form #cell-2-x:checked ~ #cell-4-o:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-5-o'],
#difficulty:checked ~ form #cell-2-x:checked ~ #cell-4-o:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-7-o'],
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-3-x:checked ~ #cell-4-o:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-3-x:checked ~ #cell-4-o:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-3-x:checked ~ #cell-4-o:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-4-o:checked ~ #cell-5-x:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-4-o:checked ~ #cell-5-x:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-4-o:checked ~ #cell-5-x:checked ~ #label-computer label[for='cell-8-o'],
#difficulty:checked ~ form #cell-3-x:checked ~ #cell-4-o:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-3-x:checked ~ #cell-4-o:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-3-x:checked ~ #cell-4-o:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-8-o'],
#difficulty:checked ~ form #cell-4-o:checked ~ #cell-5-x:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-4-o:checked ~ #cell-5-x:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-4-o:checked ~ #cell-5-x:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-8-o']
{
  z-index: 70;
  animation: none;
}

/* Prevent other player from winning! */
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-2-x:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-3-x:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-4-x:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-2-x:checked ~ #label-computer label[for='cell-1-o'],
#difficulty:checked ~ form #cell-4-x:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-1-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-1-x:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-5-x:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-4-x:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-6-x:checked ~ #label-computer label[for='cell-3-o'],
#difficulty:checked ~ form #cell-4-x:checked ~ #cell-5-x:checked ~ #label-computer label[for='cell-3-o'],
#difficulty:checked ~ form #cell-2-x:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-5-o'],
#difficulty:checked ~ form #cell-3-x:checked ~ #cell-4-x:checked ~ #label-computer label[for='cell-5-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-3-x:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-2-x:checked ~ #cell-4-x:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-7-x:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-1-x:checked ~ #cell-4-x:checked ~ #label-computer label[for='cell-7-o'],
#difficulty:checked ~ form #cell-6-x:checked ~ #cell-8-x:checked ~ #label-computer label[for='cell-7-o'],
#difficulty:checked ~ form #cell-0-x:checked ~ #cell-4-x:checked ~ #label-computer label[for='cell-8-o'],
#difficulty:checked ~ form #cell-2-x:checked ~ #cell-5-x:checked ~ #label-computer label[for='cell-8-o'],
#difficulty:checked ~ form #cell-6-x:checked ~ #cell-7-x:checked ~ #label-computer label[for='cell-8-o'] {
  z-index: 80 !important;
  animation: none;
}

/* if winning move, take it! */
#difficulty:checked ~ form #cell-1-o:checked ~ #cell-2-o:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-3-o:checked ~ #cell-6-o:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-4-o:checked ~ #cell-8-o:checked ~ #label-computer label[for='cell-0-o'],
#difficulty:checked ~ form #cell-0-o:checked ~ #cell-2-o:checked ~ #label-computer label[for='cell-1-o'],
#difficulty:checked ~ form #cell-4-o:checked ~ #cell-7-o:checked ~ #label-computer label[for='cell-1-o'],
#difficulty:checked ~ form #cell-0-o:checked ~ #cell-1-o:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-5-o:checked ~ #cell-8-o:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-4-o:checked ~ #cell-6-o:checked ~ #label-computer label[for='cell-2-o'],
#difficulty:checked ~ form #cell-0-o:checked ~ #cell-6-o:checked ~ #label-computer label[for='cell-3-o'],
#difficulty:checked ~ form #cell-4-o:checked ~ #cell-5-o:checked ~ #label-computer label[for='cell-3-o'],
#difficulty:checked ~ form #cell-2-o:checked ~ #cell-8-o:checked ~ #label-computer label[for='cell-5-o'],
#difficulty:checked ~ form #cell-3-o:checked ~ #cell-4-o:checked ~ #label-computer label[for='cell-5-o'],
#difficulty:checked ~ form #cell-0-o:checked ~ #cell-3-o:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-2-o:checked ~ #cell-4-o:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-7-o:checked ~ #cell-8-o:checked ~ #label-computer label[for='cell-6-o'],
#difficulty:checked ~ form #cell-1-o:checked ~ #cell-4-o:checked ~ #label-computer label[for='cell-7-o'],
#difficulty:checked ~ form #cell-6-o:checked ~ #cell-8-o:checked ~ #label-computer label[for='cell-7-o'],
#difficulty:checked ~ form #cell-0-o:checked ~ #cell-4-o:checked ~ #label-computer label[for='cell-8-o'],
#difficulty:checked ~ form #cell-2-o:checked ~ #cell-5-o:checked ~ #label-computer label[for='cell-8-o'],
#difficulty:checked ~ form #cell-6-o:checked ~ #cell-7-o:checked ~ #label-computer label[for='cell-8-o'] {
  z-index: 99 !important;
  animation: none;
}

/* get center in first move */
#difficulty:checked ~ form #label-computer label[for='cell-4-o'] {
  z-index: 100;
  animation: none;
}

#label-computer,
input:checked ~ input:checked ~ #label-computer,
input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer,
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer,
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer {
  display: none;
}

input:checked ~ #label-computer,
input:checked ~ input:checked ~ input:checked ~ #label-computer, 
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~  #label-computer,
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer {
  display: block;
}

label[for$='-x'],
input:checked ~ input:checked ~ #board label[for$='-x'],
input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'] {
  z-index: 1;
}

input:checked ~ #board label[for$='-x'],
input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'] {
  z-index: -1;
}






#first:checked ~ form #label-computer,
#first:checked ~ form input:checked ~ input:checked ~ #label-computer,
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer,
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer,
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer {
  display: block;
}

#first:checked ~ form input:checked ~ #label-computer,
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ #label-computer, 
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~  #label-computer,
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #label-computer {
  display: none;
}

#first:checked ~ form label[for$='-x'],
#first:checked ~ form input:checked ~ input:checked ~ #board label[for$='-x'],
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'] {
  z-index: -1;
}

#first:checked ~ form input:checked ~ #board label[for$='-x'],
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'],
#first:checked ~ form input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #board label[for$='-x'] {
  z-index: 1;
}




input[id*='-0-']:checked ~ div label[for*='-0-'],
input[id*='-1-']:checked ~ div label[for*='-1-'],
input[id*='-2-']:checked ~ div label[for*='-2-'],
input[id*='-3-']:checked ~ div label[for*='-3-'],
input[id*='-4-']:checked ~ div label[for*='-4-'],
input[id*='-5-']:checked ~ div label[for*='-5-'],
input[id*='-6-']:checked ~ div label[for*='-6-'],
input[id*='-7-']:checked ~ div label[for*='-7-'],
input[id*='-8-']:checked ~ div label[for*='-8-'] {
  display: none !important;
}

input[id*='-0-']:checked ~ #board #tile-0 div,
input[id*='-1-']:checked ~ #board #tile-1 div,
input[id*='-2-']:checked ~ #board #tile-2 div,
input[id*='-3-']:checked ~ #board #tile-3 div,
input[id*='-4-']:checked ~ #board #tile-4 div,
input[id*='-5-']:checked ~ #board #tile-5 div,
input[id*='-6-']:checked ~ #board #tile-6 div,
input[id*='-7-']:checked ~ #board #tile-7 div,
input[id*='-8-']:checked ~ #board #tile-8 div {
  display: block;
}

input[id*='-0-x']:checked ~ #board #tile-0 div::before,
input[id*='-1-x']:checked ~ #board #tile-1 div::before,
input[id*='-2-x']:checked ~ #board #tile-2 div::before,
input[id*='-3-x']:checked ~ #board #tile-3 div::before,
input[id*='-4-x']:checked ~ #board #tile-4 div::before,
input[id*='-5-x']:checked ~ #board #tile-5 div::before,
input[id*='-6-x']:checked ~ #board #tile-6 div::before,
input[id*='-7-x']:checked ~ #board #tile-7 div::before,
input[id*='-8-x']:checked ~ #board #tile-8 div::before {
  content: "X";
  background: #004974;
  color: #89dcf6;
}

input[id*='-0-o']:checked ~ #board #tile-0 div::before,
input[id*='-1-o']:checked ~ #board #tile-1 div::before,
input[id*='-2-o']:checked ~ #board #tile-2 div::before,
input[id*='-3-o']:checked ~ #board #tile-3 div::before,
input[id*='-4-o']:checked ~ #board #tile-4 div::before,
input[id*='-5-o']:checked ~ #board #tile-5 div::before,
input[id*='-6-o']:checked ~ #board #tile-6 div::before,
input[id*='-7-o']:checked ~ #board #tile-7 div::before,
input[id*='-8-o']:checked ~ #board #tile-8 div::before {
  content: "O";
  background: #a60011;
  color: #ffc7b5;
}

.tile label:hover {
  cursor: pointer;
  background: rgba(0,0,0,0.25);
}

.tile label::before,
.tile div::before {
  color: #000;
  position: absolute;
  text-align:center;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  font-size: 7.5vmin;
  font-weight: bold;
}

.tile div::before {
  padding: 100%;
}

.tile label[for$='-o']:hover::before {
  content: "O";
}

.tile label[for$='-x']:hover::before {
  content: "X";
}

#tile-0 {
  grid-column: 1;
  grid-row: 1;
}
#tile-0 label,
#tile-0 div {
  border-radius: 10% 0 0 0;
}
#tile-1 {
  grid-column: 2;
  grid-row: 1;
}
#tile-2 {
  grid-column: 3;
  grid-row: 1;
}
#tile-2 label,
#tile-2 div {
  border-radius: 0 10% 0 0;
}
#tile-3 {
  grid-column: 1;
  grid-row: 2;
}
#tile-4 {
  grid-column: 2;
  grid-row: 2;
}
#tile-5 {
  grid-column: 3;
  grid-row: 2;
}
#tile-6 {
  grid-column: 1;
  grid-row: 3;
}
#tile-6 label,
#tile-6 div {
  border-radius: 0 0 0 10%;
}
#tile-7 {
  grid-column: 2;
  grid-row: 3;
}
#tile-8 {
  grid-column: 3;
  grid-row: 3;
}
#tile-8 label,
#tile-8 div {
  border-radius: 0 0 10% 0;
}

.scrim {
  background: rgba(255,255,255,0.85);
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  display: none;
  z-index: 9;
}

#message {
  text-align: center;
  font-size: 2rem;
  line-height: 2.2rem;
  font-weight: bold;
}

#message::before {
  content: "Tied game!"
}

#message input {
  background: #000;
  color: #fff;
  font-size: 1rem;
  padding: 0.5rem 1.75rem;
  margin: auto auto;
  margin-top: 2rem;
}

input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ input:checked ~ #end,
#cell-0-x:checked ~ #cell-1-x:checked ~ #cell-2-x:checked ~ #end,
#cell-3-x:checked ~ #cell-4-x:checked ~ #cell-5-x:checked ~ #end,
#cell-6-x:checked ~ #cell-7-x:checked ~ #cell-8-x:checked ~ #end,
#cell-0-x:checked ~ #cell-3-x:checked ~ #cell-6-x:checked ~ #end,
#cell-1-x:checked ~ #cell-4-x:checked ~ #cell-7-x:checked ~ #end,
#cell-2-x:checked ~ #cell-5-x:checked ~ #cell-8-x:checked ~ #end,
#cell-0-x:checked ~ #cell-4-x:checked ~ #cell-8-x:checked ~ #end,
#cell-2-x:checked ~ #cell-4-x:checked ~ #cell-6-x:checked ~ #end,
#cell-0-o:checked ~ #cell-1-o:checked ~ #cell-2-o:checked ~ #end,
#cell-3-o:checked ~ #cell-4-o:checked ~ #cell-5-o:checked ~ #end,
#cell-6-o:checked ~ #cell-7-o:checked ~ #cell-8-o:checked ~ #end,
#cell-0-o:checked ~ #cell-3-o:checked ~ #cell-6-o:checked ~ #end,
#cell-1-o:checked ~ #cell-4-o:checked ~ #cell-7-o:checked ~ #end,
#cell-2-o:checked ~ #cell-5-o:checked ~ #cell-8-o:checked ~ #end,
#cell-0-o:checked ~ #cell-4-o:checked ~ #cell-8-o:checked ~ #end,
#cell-2-o:checked ~ #cell-4-o:checked ~ #cell-6-o:checked ~ #end {
  display: block;
}

#cell-0-x:checked ~ #cell-1-x:checked ~ #cell-2-x:checked ~ #end #message::before,
#cell-3-x:checked ~ #cell-4-x:checked ~ #cell-5-x:checked ~ #end #message::before,
#cell-6-x:checked ~ #cell-7-x:checked ~ #cell-8-x:checked ~ #end #message::before,
#cell-0-x:checked ~ #cell-3-x:checked ~ #cell-6-x:checked ~ #end #message::before,
#cell-1-x:checked ~ #cell-4-x:checked ~ #cell-7-x:checked ~ #end #message::before,
#cell-2-x:checked ~ #cell-5-x:checked ~ #cell-8-x:checked ~ #end #message::before,
#cell-0-x:checked ~ #cell-4-x:checked ~ #cell-8-x:checked ~ #end #message::before,
#cell-2-x:checked ~ #cell-4-x:checked ~ #cell-6-x:checked ~ #end #message::before {
  content: "Player won!";
}

#cell-0-o:checked ~ #cell-1-o:checked ~ #cell-2-o:checked ~ #end #message::before,
#cell-3-o:checked ~ #cell-4-o:checked ~ #cell-5-o:checked ~ #end #message::before,
#cell-6-o:checked ~ #cell-7-o:checked ~ #cell-8-o:checked ~ #end #message::before,
#cell-0-o:checked ~ #cell-3-o:checked ~ #cell-6-o:checked ~ #end #message::before,
#cell-1-o:checked ~ #cell-4-o:checked ~ #cell-7-o:checked ~ #end #message::before,
#cell-2-o:checked ~ #cell-5-o:checked ~ #cell-8-o:checked ~ #end #message::before,
#cell-0-o:checked ~ #cell-4-o:checked ~ #cell-8-o:checked ~ #end #message::before,
#cell-2-o:checked ~ #cell-4-o:checked ~ #cell-6-o:checked ~ #end #message::before {
  content: "Computer won!";
}
              
            
!

JS

              
                
              
            
!
999px

Console