how to center all body content in css code example

Example 1: css center image

.center {
  display: block;
  margin-left: auto;
  margin-right: auto;
}

Example 2: align in the middle of page html

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