<!DOCTYPE html>
<html>
<head>
<style>
.center {
margin: auto;
width: 60%;
border: 3px solid #73AD21;
padding: 10px;
}
</style>
</head>
<body>
<h2>Center Align Elements</h2>
<p>To horizontally center a block element (like div), use margin: auto;</p>
<div class="center">
<p><b>Note: </b>Using margin:auto will not work in IE8, unless a !DOCTYPE is declared.</p>
</div>
</body>
</html>https://www.w3schools.com/css/css_align.asp
<!DOCTYPE html>
<html>
<head>
<style>
.box {
display: flex;
flex-wrap: wrap;
/* Optional. only if you want the items to wrap */
justify-content: center;
/* For horizontal alignment */
align-items: center;
/* For vertical alignment */
}
* {
margin: 0;
padding: 0;
}
html,
body {
height: 100%;
}
.box {
height: 200px;
display: flex;
flex-wrap: wrap;
justify-content: center;
align-items: center;
border: 2px solid tomato;
}
.box div {
margin: 0 10px;
width: 100px;
}
.item1 {
height: 150px;
background: pink;
}
</style>
</head>
<body>
<div class="box">
<div class="item1">A</div>
<div class="item1">B</div>
<div class="item1">C</div>
</div>
</body>
</html>
https://stackoverflow.com/questions/114543/how-to-horizontally-center-a-div-in-another-div
http://www.tipue.com/blog/center-a-div/
https://stackoverflow.com/questions/2603700/how-to-align-3-divs-left-center-right-inside-another-div