Answers for "how to make a div stay 100% at the middle of the page"

center div in middle of page

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

how to align a component in the middle of page

div {
	width: 100px;
	height: 100px;
	background-color: red;
	
	position: absolute;
	top:0;
	bottom: 0;
	left: 0;
	right: 0;
  	
	margin: auto;
}