Answers for "how to put a box in the middle of the page css"

css center div in page

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

center div in middle of page

.centered {
  position: fixed;
  top: 50%;
  left: 50%;
  /* bring your own prefixes */
  transform: translate(-50%, -50%);
}