/* this will center all children within the parent element. */
.parent {
  display: flex;
  justify-content: center; /* horizontal */
  align-items: center; /* vertical */
}

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

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

IMG.displayed {
    display: block;
    margin-left: auto;
    margin-right: auto }
 ...
<IMG class="displayed" src="..." alt="...">

// example 1 
div { display: grid; place-items: center; }

// example 3
div{ display:flex; align-items:center; }

// example 3
div { width: 100%; margin: 0 auto; }

/* the simple solution*/
table {
	text-align: center;
}