使CSS箭头居中

.arrow {
  position: relative;
}

.arrow::before {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  border: solid transparent;
  border-width: 10px;
  border-top-color: #000;
}

.container {
  display: flex;
  justify-content: center;
  align-items: center;
}

.arrow {
  width: 20px;
  height: 20px;
  border: solid transparent;
  border-width: 10px;
  border-top-color: #000;
}