Answers for "how to center a div in the screen"

center div in middle of page

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

align div to center of screen

div.the-center-div {
	margin: 0 auto;
}

center element in div

/* html */
<h1>Centering with CSS</h1>

<h3>Text-Align Method</h3>
<div class="blue-square-container">
  <div class="blue-square"></div>
</div>

<h3>Margin Auto Method</h3>
<div class="yellow-square"></div>

<h3>Absolute Positioning Method</h3>
<div class="green-square"></div>

/* css */
h1,
h3 {
  text-align: center;
}

.blue-square-container {
  text-align: center;
}

.blue-square {
  background-color: #0074D9;
  width: 100px;
  height: 100px;
  display: inline-block;
}