body {
  background-color: grey;
}

#container {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  background-color: white;
}

.square {
  width: 40px;
  height: 40px;
  background-color: white;
  border: 3px solid black;
  box-sizing: border-box;
}

.square:hover {
  background-color: black;
  border: 3px solid white;
}

.button-container {
  display: flex;
  justify-content: center;
  align-items: center;
  margin: 0 auto;
}

#btn {
  margin-bottom: 10px;
  cursor: pointer;
  width: 150px;
  font-size: 20px;
}