CSS

center elements vertically in div

.container {        
    display: flex;
    align-items: center;
}

css center div vertically

.vertical-center {
  margin: 0;
  position: absolute;
  top: 50%;
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
}

css center vertically

/* 100vh = 100% Viewport Height */
body {
	display: flex;
	height: 100vh;
	flex-direction: column;
	justify-content: center;
}
/* add */ align-items: center; /*to also center horizontally.*/

vertical align center div

/* Flex */
.center {
  	display: flex;
  	justify-content: center;
  	align-items: center;
}
/* Without Flex */
.parent {
  	position: relative;
}
.child {
  	position: absolute;
  	top: 50%;
  	transform: translateY(-50%);
}

css center div vertically

<!-- if you use Tailwindcss -->
<div class="absolute top-1/2 transform -translate-y-1/2">
</div>