* {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

body {
  background: linear-gradient(to left, rgb(255, 102, 0), rgb(0, 255, 191));
  font-size: 20px;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

.heading {
  text-align: center;
  font-size: 5rem;
  margin-bottom: 3rem;
}

#red {
  color: red;
}

#yellow {
  color: yellow;
}

#green {
  color: green;
}

.gameboard {
  display: grid;
  justify-content: center;
  align-content: center;
  height: 100%;
  grid-template-columns: repeat(3, auto);
  font-style: italic;
}

.cell {
  width: 7rem;
  height: 7rem;
  border: 3px solid black;
  display: flex;
  align-items: center;
  justify-content: center;
  border-left: 0;
  border-bottom: 0;
  cursor: pointer;
  font-weight: bolder;
  font-size: 6rem;
}

.cell:last-child,
.cell:nth-child(3),
.cell:nth-child(6) {
  border-right: 0;
}

.cell:first-child,
.cell:nth-child(2),
.cell:nth-child(3) {
  border-top: 0;
}

.turn-text {
  font-size: 3rem;
  font-weight: bolder;
  font-family:
    Impact,
    Haettenschweiler,
    'Arial Narrow Bold',
    sans-serif;
  text-align: center;
  margin-top: 3rem;
}

.winning-box {
  display: none;
  position: fixed;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: rgba(0, 0, 0, 0.9);
}

.winning-box.appear {
  display: flex;
}

.winning-text {
  font-size: 4rem;
  font-weight: bolder;
  color: white;
}

#restart {
  cursor: pointer;
  display: block;
  font-size: 3rem;
  padding: 0.5rem 1.3rem;
  border: 1px solid black;
  margin: 0 auto;
}

#restart:hover {
  color: white;
  background-color: black;
  border: 1px solid white;
}

@media only screen
  and (min-width: 479px)
  and (max-width: 780px) {
  .cell {
    width: 6rem;
    height: 6rem;
    border: 3px solid black;
    display: flex;
    align-items: center;
    justify-content: center;
    border-left: 0;
    border-bottom: 0;
    cursor: pointer;
    font-weight: bolder;
    font-size: 5rem;
  }

  .heading {
    font-size: 4.5rem;
    margin-bottom: 2.5rem;
  }

  .turn-text {
    margin-top: 2.5rem;
  }
}

@media only screen
  and (min-width: 320px)
  and (max-width: 480px) {
  .cell {
    width: 5rem;
    height: 5rem;
    border: 3px solid black;
    display: flex;
    align-items: center;
    justify-content: center;
    border-left: 0;
    border-bottom: 0;
    cursor: pointer;
    font-weight: bolder;
    font-size: 4rem;
  }

  .heading {
    font-size: 3rem;
    margin-bottom: 0.6rem;
  }

  .turn-text {
    margin-top: 1rem;
  }
}