site.css

html, body {
  width: 100%;
  height: 100%;
}

body {
  font-family: 'Avenir', Helvetica, Arial, sans-serif;
  margin: 0;
  background: rgb(250, 250, 250);
}

#root {
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
}

#controls {
  width: 300px;
  text-align: center;
  margin: auto;
  margin-bottom: 22px;
}

#board-container {
  display: flex;
  flex-wrap: wrap;
  width: 300px;
  height: 300px;
  background: white;
  border: 0.5px solid rgb(200, 200, 200);
}

#board-container .cell {
  width: 100px;
  height: 100px;
  text-align: center;
  line-height: 100px;
  font-size: 32px;
  font-weight: 500;
  margin: 0;
  border: 0.5px solid rgb(200, 200, 200);
  box-sizing: border-box;
  cursor: pointer;
  transition: 0.2s;
}

#board-container .cell:hover {
  background: rgb(250, 250, 250);
}

#copyright {
  font-size: 14px;
  color: rgb(100, 100, 100);
  text-align: center;
}