style.css

body {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: linear-gradient(to right, blue, cyan);
  color: white;
}

td {
	border:  4px solid rgb(255, 255, 255);
	height:  100px;
	width:  100px;
	text-align:  center;
	vertical-align:  middle;
	font-family:  "Comic Sans MS", cursive, sans-serif;
	font-size:  70px;
	cursor: pointer;
}

table {
	border-collapse: collapse;
}

table tr:first-child td {
	border-top: 0;
}

table tr:last-child td {
	border-bottom: 0;
}

table tr td:first-child {
	border-left: 0;
}

table tr td:last-child {
	border-right: 0;
}

.endgame {
  font-family: sans-serif;
  display: none;
  width: 200px;
  background-color: rgba(96, 205, 63, 0.8);
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  padding-top: 50px;
  padding-bottom: 50px;
  text-align: center;
  border-radius: 5px;
  color: white;
  font-size: 2em;
}

button {
  color: white;
  background-color:rgb(0, 132, 255);
  font-family: sans-serif;
  border: none;
  outline: none;
  font-size: 1.2rem;
  padding: 0.8rem 1.4rem;
  margin: 1rem;
  border-radius: 20px;
}