html {
    box-sizing: border-box;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    background-color: #eee;
    color: #1a1a1a;
    font-family: 'Open Sans', sans-serif;
  }
  
  *,
  *:before,
  *:after {
    box-sizing: inherit;
    -webkit-box-sizing: inherit;
    -moz-box-sizing: inherit;
  }
  
  body {
    display: grid;
    justify-content: center;
    align-items: center;
    min-height: 95vh;
    text-align: center;
  }
  
  .board {
    display: grid;
    grid-template-columns: repeat(3, auto);
    margin: 30px auto 40px auto;
  }
  
  .square {
    width: 100px;
    height: 100px;
    border: 2px solid #1a1a1a;
    transition: 0.2s ease-out;
    cursor: pointer;
    position: relative;
  }
  
  /* change color of square when hovering */
  .square:hover {
    background-color: #ddd;
  }
  
  /* to disable the hover effect when a square is already selected
      or when the game is over */
  .gameOver .square:hover,
  .square.X:hover,
  .square.O:hover {
    background-color: inherit;
    cursor: default;
  }
  
  /* display outline and foreground overlapping and center contents */
  
  .square .outline {
    position: absolute;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100px;
    width: 100px;
  }
  
  .square .foreground {
    position: absolute;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100px;
    width: 100px;
  }
  
  /* outline and foreground of a square with X */
  
  .square.X .outline:before {
    content: "";
    background: #1a1a1a;
    width: 14px;
    height: 58px;
    position: absolute;
    transform: rotate(45deg);
    z-index: 2;
  }
  
  .square.X .outline:after {
    content: "";
    background: #1a1a1a;
    width: 14px;
    height: 58px;
    position: absolute;
    transform: rotate(-45deg);
    z-index: 2;
  }
  
  .square.X .foreground:before {
    content: "";
    background: #f03a17;
    width: 8px;
    height: 52px;
    position: absolute;
    transform: rotate(45deg);
    z-index: 3;
  }
  
  .square.X .foreground:after {
    content: "";
    background: #f03a17;
    width: 8px;
    height: 52px;
    position: absolute;
    transform: rotate(-45deg);
    z-index: 3;
  }
  
  /* outline and foreground of a square with O */
  
  .square.O .outline:before {
    content: "";
    background: transparent;
    width: 58px;
    height: 58px;
    position: absolute;
    border-radius: 50%;
    border: 14px solid #1a1a1a;
    z-index: 2;
  }
  
  .square.O .foreground:after {
    content: "";
    background: transparent;
    width: 52px;
    height: 52px;
    position: absolute;
    border-radius: 50%;
    border: 8px solid #0082a5;
    z-index: 3;
  }
  
  /* hide outer borders of the squares */
  
  .square:nth-of-type(1),
  .square:nth-of-type(2),
  .square:nth-of-type(3) {
    border-top: none;
  }
  
  .square:nth-of-type(1),
  .square:nth-of-type(4),
  .square:nth-of-type(7) {
    border-left: none;
  }
  
  .square:nth-of-type(3),
  .square:nth-of-type(6),
  .square:nth-of-type(9) {
    border-right: none;
  }
  
  .square:nth-of-type(7),
  .square:nth-of-type(8),
  .square:nth-of-type(9) {
    border-bottom: none;
  }
  
  /* new game button */
  
  button {
    background-color: #008888;
    font-family: 'Open Sans', sans-serif;
    font-size: 14px;
    color: white;
    border: none;
    padding: 12px 16px;
    border-radius: 4px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.16), 0 2px 5px rgba(0, 0, 0, 0.26);
    transition: 0.2s ease-out;
    cursor: pointer;
  }
  
  /* change color and shadow of button when hovering */
  button:hover {
    background-color: #009999;
    box-shadow: 0 10px 20px rgba(0, 0, 0, 0.16), 0 5px 6px rgba(0, 0, 0, 0.26);
  }