水平居中浮箱

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

.container {
  display: grid;
  justify-content: center;
}

.container {
  margin-left: auto;
  margin-right: auto;
}

.container {
  position: relative;
  left: 50%;
  transform: translateX(-50%);
}

.container {
  text-align: center;
}