好吧，试试用这个css：

body {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0;
}

.container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 80%;
  width: 80%;
}

.grid {
  display: flex;
  flex-wrap: wrap;
  width: 60%;
  height: 60%;
  margin: 0 10%;
}

.square {
  width: 20%;
  height: 20%;
  border: 1px solid black;
  box-sizing: border-box;
  margin: 1%;
  border-radius: 5px;
}

.selector {
  width: 20%;
  height: 60%;
  display: flex;
  flex-direction: column;
  align-items: center;
  margin: 0 10%;
}

.bet-amount {
  margin: 5%;
}

.button {
  margin: 5%;
}