<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>FlexBox Tutorial</title>
</head>

<body>

  <div class="container">
    <div class="box box1">1</div>
    <div class="box box2">2</div>
    <div class="box box3">3</div>
    <div class="box box4">4</div>
    <div class="box box5">5</div>
    <div class="box box6">6</div>
    <div class="box box7">7</div>
    <div class="box box8">8</div>
    <div class="box box9">9</div>
    <div class="box box10">10</div>
  </div>
</body>

</html>
/* CSS Normalize */
article,aside,details,figcaption,figure,footer,header,hgroup,nav,section,summary{display:block;}audio,canvas,video{display:inline-block;}audio:not([controls]){display:none;height:0;}[hidden]{display:none;}html{font-family:sans-serif;-webkit-text-size-adjust:100%;-ms-text-size-adjust:100%;}a:focus{outline:thin dotted;}a:active,a:hover{outline:0;}h1{font-size:2em;}abbr[title]{border-bottom:1px dotted;}b,strong{font-weight:700;}dfn{font-style:italic;}mark{background:#ff0;color:#000;}code,kbd,pre,samp{font-family:monospace, serif;font-size:1em;}pre{white-space:pre-wrap;word-wrap:break-word;}q{quotes:\201C \201D \2018 \2019;}small{font-size:80%;}sub,sup{font-size:75%;line-height:0;position:relative;vertical-align:baseline;}sup{top:-.5em;}sub{bottom:-.25em;}img{border:0;}svg:not(:root){overflow:hidden;}fieldset{border:1px solid silver;margin:0 2px;padding:.35em .625em .75em;}button,input,select,textarea{font-family:inherit;font-size:100%;margin:0;}button,input{line-height:normal;}button,html input[type=button],/* 1 */
input[type=reset],input[type=submit]{-webkit-appearance:button;cursor:pointer;}button[disabled],input[disabled]{cursor:default;}input[type=checkbox],input[type=radio]{box-sizing:border-box;padding:0;}input[type=search]{-webkit-appearance:textfield;-moz-box-sizing:content-box;-webkit-box-sizing:content-box;box-sizing:content-box;}input[type=search]::-webkit-search-cancel-button,input[type=search]::-webkit-search-decoration{-webkit-appearance:none;}textarea{overflow:auto;vertical-align:top;}table{border-collapse:collapse;border-spacing:0;}body,figure{margin:0;}legend,button::-moz-focus-inner,input::-moz-focus-inner{border:0;padding:0;}

/* Box-sizing border-box */
* { -moz-box-sizing: border-box; -webkit-box-sizing: border-box; box-sizing: border-box; }


/* Some default styles to make each box visible */
.box {
  color:white;
  font-size: 100px;
  text-align: center;
  text-shadow:4px 4px 0 rgba(0,0,0,0.1);
  padding:10px;
}

/* Colours for each box */
.box1 { background:#1abc9c;}
.box2 { background:#3498db;}
.box3 { background:#9b59b6;}
.box4 { background:#34495e;}
.box5 { background:#f1c40f;}
.box6 { background:#e67e22;}
.box7 { background:#e74c3c;}
.box8 { background:#bdc3c7;}
.box9 { background:#2ecc71;}
.box10 { background:#16a085;}


/* We start writing out flexbox here. The above is just page setup */
.container {
  display: flex;
  border: 10px solid mistyrose;
  height: 100vh;
  flex-wrap: wrap;
  align-content: flex-start;
/*   justify-content: center;
  justify-content would help 10 stay in the center */
}

.box{
  width:33.333%;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.