居中

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

.center-grid {
  display: grid;
  place-items: center;
}

.center-transform {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.center-margin {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  margin: auto;
  width: 200px; /* 需指定宽度 */
  height: 100px; /* 需指定高度 */
}

.center-table {
  display: table-cell;
  text-align: center;
  vertical-align: middle;
  width: 100vw;
  height: 100vh;
}
.center-table-child {
  display: inline-block;
}

.center-calc {
  position: absolute;
  top: calc(50% - 50px); /* 减去高度的一半 */
  left: calc(50% - 100px); /* 减去宽度的一半 */
  width: 200px;
  height: 100px;
}

.center-flex-alt {
  display: flex;
}
.center-flex-alt-child {
  margin: auto;
}