index.css

body {
  margin: auto;
  width: 100%;
  max-width: 1200px;
  text-align: center;
  font-family: 'Arial';
  font-weight: bold;
  background-color: #020202;
  color: white;
}

h1 {
  font-size: 60px;
  color: #2cbb05;
  margin-left: 20px;
}

#gameGrid {
  display: grid;
  grid-template-columns: auto auto auto;
  margin: 20px auto;
  width: 95%;
}

.gameField {
  border: 8px solid #2cbb05;
  color: white;
  font-size: 100px;
  padding: 15px 0px;
  text-align: center;
  height: 110px;
  cursor: pointer;
}

.gameField:nth-child(-n+3) {
  border-top: none;
}

.gameField:nth-child(n+7) {
  border-bottom: none;
}

.gameField:nth-child(3n) {
  border-right: none;
}

.gameField:nth-child(3n+1) {
  border-left: none;
}

button {
  background-color: #2cbb05;
  font-family: 'Montserrat';
  font-weight: bold;
  font-size: 16px;
  color: white;
  margin: 50px;
  width: 130px;
  height: 60px;
  border: none;
  display: inline-block;
}

#header {
  display: flex;
  justify-content: center;
  align-items: center;
}

#message {
  background-color: whitesmoke;
  padding: 18px;
  font-size: 30px;
  box-shadow: 0px 0px 25px 0px #2cbb05;
  color: #2cbb05;
  transition: all .4s ease-in-out;
  animation: scaleMessage 1.6s infinite;
  display: none;
}

@keyframes scaleMessage {
  50% {
    transform: scale(0.8);
  }

  100% {
    transform: scale(1);
  }
}